you are correct Carl, it is a no no. but the same rings true in reverse. The only way this would be acceptable is if the head was off, and the water would be poured around the cyl liners. Pouring the water into the water pump will accomplish absolutely nothing except possibly crack or warp the aluminum housing.
The bottom line is this. by adding hot water or any temperature differential, you’re introducing expansion and/or contraction. Aluminum is right up there with copper when it comes to absorbing and distributing heat. through out the entire piece. Not really an issue unless there isn’t any where for the expansion to take place (bolted down) then it cracks or warps - especially cast aluminum, magnesium, and Iron. Cast aluminum is strong in compression, but has very little tensile strength; which makes it prone to cracking and breaking as does cast iron and magnesium for the same reasons. This has to do with the additives to the aluminum when casting to make the internal grain structure stronger. In contrast where as, extruded aluminum gets its strength thru the oxide layer on the outside of the aluminum - which provides more tensile strength put less compression strength. There are other factors that play into the strength of aluminum that I’m not going to talk about because I’d wear my finger tips off, and honestly who cares.
Anyway, in order to get the engine to turn over, the best way is to reduce the forces that are keeping it from turning over. Disable as any ancillary unnecessary friction (pully driven accessories), and compression - pull the plugs (I know it’s a huge PITA, but it maybe the quickest solution to the end result).
I image since the crank pulley bolt has been loosened it won’t tighten up enough. Check to make sure the bolt isn’t stretched. pull it out, and examine the threads. the threads should be evenly space. a good way to check this is run a thread chaser or nut up the entire threaded part. If the nut hangs up, or is hard to turn, then chances are the bolt is stretched. Replace the bolt.
if the threads check out fine, then I’d put A DROP of non permanent thread lock on the bolt and tighten it down to spec. give it 24 hours and the try again.
I know it’s a PITA to loosen all of the belts, by doing so, you’re reducing the amount of items that could be keeping the engine from turning over. Once the engine turns over, its a process of elimination of identifying what is one isn’t spinning. I had this issue with my XJS and the air pump. The air pump siezed. Oh, darn I had to take it off. haha
Just curious, have you checked the oil? is there any sign of moisture on the dipstick sludge? rust? also
Pop off the filler cap, look at the back side see if there’s any signs of moisture, also take a peek at the cam, is there any rust on the camshaft? Have you pulled a spark plug to see if there is any rust?
All of the above are good indications of the internal condition of the engine.
If I was suspect of seized rings, I’d put a bit of penitrating oil down the spark plug holes.
Keep us posted