Hi Lewy, sounds like an interesting project you have there!
I seem to remember reading an article in Auto Italia a few years back about a 1 off 246 replica that a chap had built for himself, it seems the experts at the magazine thought it was pretty authentic too.
As for a Dino engine, you could try
www.eurospares.co.uk as they break italian exotics and sell a lot of new parts for said cars.
Regards
Jon