Compared to the shipping weight of 350 lb for a fully dressed air cooled six in a crate, an Olds 455 at 620lbs, (fully dressed, no flywheel), is a lot of extra weight in a compact.
That’s about the same as a Buick 455, a Ford 460 and just a lighter than the Pontiac. I know the late emissions blocks all had more windows in the webbing with other weight and performance cutting, but had not ever heard of the tall deck Olds blocks being called light weight blocks. The diesel blocks are heavier.
Have you lifted the cast iron intake manifold off one?
My stock cast iron 330, 4 BBL Olds intake felt as heavy as a whole 1979 302. (OK, Almost. There is a lot of metal in that intake, and even the Edelbrock replacement was a lot of metal to carefully set in place without help.)
Anyway, 500 ft lb of torque would be worth the extra weight.