Looks like either the intake manifold is machined too low where the distributor sits(or excessive block/head milling), or the distributor housing collar is machined too high(Chinese?) and the distributor shaft is jammed hard against the oil pump drive rod bottoming everything out. I'd want to inspect the pump now too, for scoring of the end plate and end of gears.
Oil pump drive rod could be too long also, there are three lengths that all look the same to the eye but with 1/8" or so difference - standard SBC, SBC w/BBC pump(slightly shorter), and BBC(longer), but I would be looking at distributor height first for manifold ot housing problems.
Moroso sells a distributor to manifold shim kit for this reason, did you check at assembly that the pump, drive rod, and distributor all had adequate end play??
Gear appears to show distributor sitting too deep in the block also.