The "Rope Trick" did not work for me. The heads bind on stop leak that deposits in the space between the stud shanks and the holes for them in the head.
There are a couple of choices.
I recommend going to
WWW.JagLovers.Org and downlading Kirby Palm's free book "Help For The XJS Owner". In it is a drawing for a head removal tool that requires the cam shaft be removed and bolts to the studs for the camshaft bearing caps.
The other way, the way I did it is a lot less pleasant. I used a bottle jack (six inch high 15 cm body) and walked the head up bu catching the coener on the webbing of the block and pushung against the freeze plugs in the head. I used wood shims to keep the head from coming back down on the end just raised. This is slow, tedious, frustrating and risks chipping the aluminum bosses for the freeze plugs. I used a crow bar and i/4" plywood shims, stacking them on op of each other as I slowly walked the head up the studs. DO NOT ALLOW THE STEEL PRY BAR TO BEAR DIRECTLY AGAINST THE ALUMINUM OF THE HEAD!!!
After, I used gun bore cleaning brushes to clean the crud out of the stud bore holes and used a lot of scotchbrite pads to clean the corrosion, dried stop leak off the studs.
You can try penetrating oil, but the nature of the stop leak prevents it from soaking the 4 inches needed.
I have removed three sets of heads this way. Next Time, if there is a next time, I want to try the tool in Palm's book.
Persitance pays. Take your time. Coat the studs with red electrical varnish after they have been cleaned.
Good luck.