Struggling with XJ550 rear engine bolt removal

Hi all, first post here.
I've just got my '81 550 and am trying to strip everything down for restoration. I'm stuck trying to get the engine out. The bike has sat unridden for almost 2 decades and while I've got the nut off the rear engine mount, it appears that the bolt has seized onto both the spacer in between the engine castings, as well as one of the sleeves inside the rubber bushings.
It spins reasonably freely, but no amount of oil / heat / hammering seems to have shifted the bolt out even slightly. Does anyone have any tips on how I might be able to get it freed up? Will also consider destructive methods and replacing the parts at this point!

 

Have you enough thread undamaged so you can jack it out against the mounting?
The issue is not uncommon, I have a 650 turbo engine mated to part of a frame, for the very reason you have.
If you go all ape at it there is a risk of breaking the casings, hence the jacking against the mount and pulling it through everything. If you have no thread, or no way to make suitable spacers, you have no choice but to get someone with a plasma cutter in to remove it....