I already had the engine out and was rebuilding it. When I say the last step I was referring to getting something that could get that plug really hot to break the corrosion free. I didn’t need to resort to that because I was able to work the studs out without breaking them. Three weeks, two to three times a day application of penetrating oil, taps to the end of the stud with a hammer, and a stud puller. You are past that point with your one stud (perhaps not the others), so you are going to have to go further than I did. You can also pull the rest of the freeze plugs out so you can work more directly with the remaining studs. I’m thinking that if you had one stud in condition to break the rest are likely not far behind them, and the problem is only going to get worse the longer you wait. To see what is going on with the stud you could resort to an endoscope, they have gotten really cheap. The one I got is small enough to go down the stud hole into the block and look (and I think it cost me $12). That way you can make an informed decision if this task is in your wheelhouse, or if you should pallet this thing up and let an expert take it.
I have removed these from Ford big bock race engines. Heat, tapping around the perimeter pretty hard, Kroil, repeat. Be sure not to bugger the hex!
Can anybody confirm that it is a normal thread (leftie, loosie - righty, tighty) and not a left hand thread ?
Just want to be sure before I crank on it.
Jay
I would be 99% certain that its a conventional thread, I’ll see if I can identify the threads on my engine which a)is out of the car and b) has the heater element installed so I might be able to view the threads.
Make that 100% sure it’s right hand. It’s a standard right hand thread. Otherwise as you tighten the head nut there would be a risk of loosening the lower thread. I suspect you will need to pull the engine and send it out IMHO.
Sorry I may not have been clear Bill, we were talking about the heater element blanking hex nut installed in place of the freeze plug on the side of the S2 engine block. I need to remove it to gain access so wanted to check it was a standard thread.
Robin, if you get a chance could you also post a picture of the heater element that is sometimes installed, as I have no idea what it is.
Jay
OK, now I am also at 99.9%. Most threads are right hand unless there is an engineering need for otherwise, like the wheel knock offs.
I’m rooting for you Jay. The odds are with with you.
Normal thread but don’t worry unduly. It is no help to remove as there is just space behind it and all the stud stuff happens behind the ten core plugs. A long long tube over a 3/4” drive breaker bar and socket does the job but it’s not 100% essential as it’s not usually a sludge trap that high up.
That is the issue. I need to get to the stud behind the hex fitting as that is the one that has broken off. The hex fitting is fitted in the location where the core plug would be. I tried an endoscope down the stud hole but it is difficult to see what is going on. So hoping removing the hex plug will at least let me get more visibility into the stud break.
Jay
Jay. If I can offer a suggestion you are probably only going to get one good chance at removing this plug. If you rush it chances are you will round off the socket and then things become more complicated. You need to devise a method to get that plug soaked with penetrating fluid and keep it soaking for at least 2 weeks before violent action. I think you are going to have to pull the engine to do this job properly. Lay the engine on its side with the plug up. Pack cotton wool, cloth etc around the plug and then soak the material with your penetrant of choice. I like acetone/ATF. It has worked for me where others have not and it is cheap. Resoak the material daily and cover the area with an old coffee cup to slow down evaporation of the acetone. If you have access to a torch periodically heat the plug .(clean up all fluid before each heating. It is flammable). After 2 weeks then use your big air impact or a long breaker bar. While the engine is out you can then attend to the rest of the studs. I would remove the rest of the frost plugs and soak each of the studs before attempting to remove them. Time is your friend with penetrating fluids. Give it lots of time to creep.
I will add to Geoff’s good advice, except I don’t know that an engine pull would be necessary. I do agree they all should be replaced, one at a time.
Well I have been adding penetrating oil, heating with a propane torch and using a long breaker bar with about 3 ft arm but have not been able to remove the plug. I also tried a 1/2 impact wrench but did not budget. At this point I have decided to remove the engine so I can get better access.
Plan is to continue to spray with penetrating oil, and heat and then try a much longer arm and hang a bucket of bricks or similar from it for a few days. May also try renting a 1" impact wrench for a bit more oomph (technical term).
Any success stories of people removing this plug would be helpful at this time as it feels like I am banging my head against a wall 
.
Jay
Worst case you could drill, and carefully cut out the plug, cut just short of threads, crack it out with a punch, or cold chisel.
All I can add is that I’ve been told you can sometimes break a fastener loose by first trying to move it opposite the rotation you would use to loosen it. I don’t see why the same wouldn’t apply to the plug in question.
More specifically, drill a half inch hole in the center of the lug. Cut with hacksaw blade, dremel, mini grinder, or whatever, an “x” just to the threads. Then take a punch, and tap hard next to the drill hole on the remaining wedges. One will cave in, the rest will pull right out. It’s not as hazardous as it sounds.
Note this is a screw in steel plug (see earlier photo) and not the normal freeze plugs, so it is not possible to knock it out with a punch. Cutting and taking out the parts is a last resort option if the 7/8" hex key rounds off, but hopefully it won’t come to that.
Got to get the engine out first which is in process, but some bolts have not been touched in 50 years so taking a while to get stuff off, like the exhaust.
Jay
Jay, yes, I know it is the screw out plug. It can be drilled and parted out.
My fault, I misread your response. I saw the “One will cave in, the rest will pull right out.” and thought freeze plugs, but you were talking about the parts of the steel plug. Its been a long day 
Hi Jay…have you considered welding a nut onto the plug…the heat could possibly break the seal and give you a better head to fix a tool to undo…Steve