Hop on over to the 351C forum and see some of the stuff that I do with the 393/408C engines.
I love the Cleveland stuff and can make excellent power with even cast iron 4V heads (and I currently have some here in the shop).
As for the T5, don't expect it to live long, World Class or not. Cobras are traction limited, so that's in your favor, but if it ever hooks up on a wide open throttle upshift, you're spitting parts out. These things explode behind factory 5.0 Mustangs.