Hi all.
I will get to the point but I thought id just give you some background info.

So I have a really nice, Very unique XJ40 3.2s. I think it's some sort of limited/special edition (can't find any info) as it is this really strange black/brown/red/purple colour (it looks different in every light), its got red carpet throughout and its on gold wheels, a colour and style that I've never seen on any other jag. I thought for a long time that someone must have modified it but the more I look at it, the more I think it has come from the factory like that.
I'm going to get it washed and take some pics for you guys tomorrow. I'm hoping one of you will have some info on it for me

This is not my normal cup of tea when it comes to styling but I just can't help but love it on this car. It turns heads everywhere it goes and its just a pleasure to be in. I was given it buy a friend and I was using it for while but it developed some issues. It sprung a major oil leak and ran very low on oil. It now sounds a little top end rattley and is smoking so I think it may have cooked the head, stem seals etc.

As much as I love it, I just couldn't justify fixing it and driving it as it is soo bad on fuel and it just doesn't offer the performance in return. I have no problem with cars that drink fuel, so long as they go like stink. This absolutely does not!
Anyway, I parked it up and its been there 2 years. I was on the cusp of buying an S-type R last month but this virus put a stop to that. Since then, I got thinking, why buy an S-type when I have this really cool XJ40 that I could do something with. If I can get, modern performance, packaged in this old jag then that is my dream car! I had intended to do a LS or LT engine swap if the distant future but I think there is another option that keeps it a true Jaguar for a fraction of the cost.

So, here is my plan (what I have been thinking about for at least the last hour)… stick a 4.2 supercharged v8 in it.

Can you guys help with info on the following:

I am under the impression that the XJ40 chassis is pretty much identical to the later X300 and X308 cars? If not identical, what are the differences and do they differ when it comes to mounting points for suspension and subframes?
If the above is true then am I right in thinking that the front and rear subframes are interchangeable? Can I simply bolt in the subframes from an X308 XJR and run XJR suspension, hubs, brakes etc?
If the subframes simply bolt in then that means that the 4.0 supercharged engine should simply, drop in and if the bulkhead is the same then the gearbox should also fit?

Next question:

If the 4.0 fits, then can the same be said for the 4.2 supercharged? Is it the same as the 4.0 supercharged bottom end? Obviously, I am aware that the displacement is different, but is that from bore size /stroke changes. Externally, are they the same block with the same mounts?
Are there any differences across the jaguar model line up with this engine? i.e. did the XKR get more power from differences in the engine internals? Is there a specific model and year that received better internals?

Next question:

The gearbox on the 4.2 is different to the 4.0 right? Are they different in size and shape or is it just different internally? If external, do any of you think that there would be an issue with clearance?
I believe the xkr 4.2 has a flappy paddle box but the xj and s-type don't? I think it would be cool to have an xj40 with flappy paddles.

I think that will do for now. I don't want to get too invested in the idea if you guys all scream at me that its totally incompatible or requires a lot more work than I'm thinking it would take.

Thanks for you time!