There is no comparison between Rocket and Little M. Little M is a very good block, made as a "replacement" block for the 400, only "tough". Rocket is a RACE block. Yes, ProStock Truck is where it was most widely used, IIRC. Virtually everything for Rocket is either custom made or hard to find. That's the "price" of a true race engine. Even a Chevy. Many big block components "fit", as I recall. A custom crank is needed to use the BBC timing set. There's probably some sort of sleeve assembly to make it work if not a "blown" application.
So, if you're looking for the least expensive way to make "big" power and "live", Rocket is probably not for you. If you want the ULTIMATE in SBC technology and the most "bang", regardless of "buck", Rocket is the way to go.