the 366 is a GMC engine, not a chevy, It outweighs a big block chevy, and usually has a cast steel crank
That's not actually correct. It is a Chevy engine, a variant of the MK4 big block to be exact. GMC didn't start using them until the late '60s when they went to using Chevrolet engines in their trucks, and even then they used their 60 degree V6 and V8s up to the early '70s. As to the increased weight, that is due to the taller deck hight ans wider intake manifold. Also, I have seen them with both cast and forged cranks.
