So, I'm thinking of building another one but likely to be the Haynes chassis as gave away the RC book.

I'll be going slightly oversize again. I have a complete BMW 3 series rear end and a HP 45 auto.

Do I go V8 (BMW 4 / 4.4) or diesel (also BMW but 2l)

Thoughts?

V8!

Go with whichever one you want to go with, as long as it has eight cylinders and runs on petrol...