Yes perhaps the motor is unhappy about its alternate sports car body. Personally I think it should be proud to be housed in its slick new body

Now for 2500's yes they are hell boring in standard form but I've got a heavily modified one and it's seriously fun. It gives plenty of new cars a run for their money.

The spitfire has been a total bitch to get together but it's starting to look worth it. I'm really curious to know how the GX motor will get along.

Coops: The TR4 became the TR5 later on and hence it is certainly big enough to take the triumph 6 cyl motor. Thus I would imagine that almost anything would fit in there as long as it's not too wide. (given that the triumph 6 cyl is reallly very large for its small capacity (block is bloody heavy and too thick))

One of my buddies has a dolly sprint in modified form (with standard motor) and it is often off the road for fixes but very nice when running.

Yes you can certianly do conversions for nissan rear ends (or subaru).