O.K., so I finally got the new (resin) radiator outlet pipe assembly on tonight (btw, the thermo. housing looks O.K.), only to then discover that I have another major coolant leak running down the firewall. Won’t know for sure until I get the car jacked up tomorrow, but I suspect it’s going to be a leaking heater core, esp. since I couldn’t get any heat out of the heater earlier on. Of course, it can be bypassed, but then no heat for the rest of the winter (except for the seat heaters) 
Is this a common problem with the XJ8s? What in the world did Jag make the cores out of anyway? Before they were always brass or some other metal that did not corrode (same for the radiators) … 
Don’t know about heater cores for the XJ8. Never had to replace one. I did MANY heater hoses behind the throttle assy. (the large cluster of hoses above the gearbox bellhousing)
I replaced many XJ-S, Series I, II, and III XJ6 as well as the XJ40. They were all brass but clogged or leaked so nothing is forever.
The XJ40 was the easiest to slide out the side.
bob