So I've spent some time searching and can't find anything on this specific scenario. Apologies if this has been covered elsewhere. Right now I'm looking at a screaming deal on a 1998 XK 4.0 which I am very tempted to pull the trigger on. Only hangup is that I've been led to believe that the 4.0 is more problematic than the 4.2 plus I've grown accustomed to the power my 2003 STR has. It got me thinking about taking the engine, transmission, and any necessary wiring and computers from the S and putting them in the XK. Would that be possible or even worthwhile? I know the easiest thing would be to find an XKR and just buy that, but I know the condition of the engine and trans in my STR and they are well sorted (knock on wood). Also the insanely low price on the XK plus the fact that I have (hopefully) all of the parts I would need on hand already are really the only reason I'm entertaining this.

Ideally I'd like to swap everything out, debadge the S and sell it. I feel as though it should work in theory, but I know from having read some other threads that sometimes there are communication difficulties when changing modules from different vehicles. Has anyone done anything like this? Would the immobilizer throw a fit if it saw an ECU it doesn't recognize and is there a way to make it happy? Is this a dumb enough idea that I should just sell the S as is and start saving my pennies for an XKR and hope that it's in close to as good of shape mechanically as my S is?