A 4.0 or, preferably, a 4.2 Jaguar V8 may fit but then you have everything else to change.
I'd stick with a 4.0 AJ6 or AJ16, but that's me.

 

Hi Maxpanch,

Welcome to the Jaguar Forums! It's great to have you with us.

Roger's advice is sound. Fitting anything other than an AJ6 engine will require replacing many other systems or developing solutions to many problems that will arise. Even an AJ16 from an X300 will require an entirely different Engine Managment System.

One point in your favor is that the 3.2L cars use the hydromechanical ZF 4HP22 transmission instead of the electronically-controlled 4HP24 in the 4.0L cars.

On the other hand, the differential gear ratios were different between the 3.2L and 4.0L, so you'd have to sort that out.

Thinking out loud, I think the primary differences between a 3.2L and 4.0L are the crankshaft, pistons and connecting rods. I believe the block, head, cams, valves, air intake and other components are the same. If you could find a 4.0L engine with a burned valve or such, you could put your head on the 4.0L block.

AJ6 Engineering has developed some upgrades for the AJ6 engine that you might want to check out:

aj6 engineering | For the Jaguar enthusiast

and their older site:

WELCOME TO AJ6 ENGINEERING / AJ6 Engineering

And here's an account of upgrading a similar engine in an XJS:

Problems with AJ6 "sort of Engineering" TOILET TUNE

Cheers,

Don