I had a 76 Chevy full size pickup that would spin the tires on dry pavement. Had a 350 with TH350 automatic. Everything was stock on it.
So yours should do better than it appears to be doing. 300hp even in that truck would get it moving quite well. May not be big block, but sounds like it should do better than it is.
I agree that it sounds like carburetor is not delivering the fuel it needs at low speed. Once into the high speed circuits they sound like they are working. The ignition timing could be off too.
