Thanks Tom, I could not seem to come up with the bore for the '58 GMC 336. I see I had the 100ths mixed up between the '58 crank throw and the '58 main sizes. I was going from memory and I should have looked it up first. Old timers disease hits again.
I built my 406 from the early '60 block because it is a lot stronger than later blocks. I was thinking along the same lines using the '58 336 block. Smaller bore, lighter reciprocating weight, wider deck between bores, and the stronger block. Other than the bell housing and starter adapting, it would be a well built easy build. My 406 rotating weight came out at 2000 with aluminum rods. The smaller piston along with a good set of steel rods should still come out at or lighter. This is just a thought experiment. Something I might play with on the side if I can find a good 336 block. Even a '59 336 block would be something to play with. With an even smaller bore but the 3 inch mains, it would open up more options for aftermarket cranks, and good available main bearings. The only problem is the really small bores and matching heads/chambers/valves to that small of a bore. Again, just brain storming.
Now dats sompin' differnt.