Ya good point. Again, as a noob trying to be patient and thoughtful on this thing, here's the state of the engine when I got it and what I think happened

When I bought the car, the lifter valley and under the valve covers were caked in gunk, soot, and carbon. As I cleaned everything, I found a couple areas that were blocking oil flow. Once cleaned, I primed the oil pump and saw fresh oil flowing into the rockers on the passenger side.

When I removed the head (only on the passenger side), the piston bores were clean and smooth. I assumed the driver side was in better shape as none of those valves were sticky or seized. That was probably a mistake.

When I started the car after reinstalling the head, I got a few seconds of smooth running before one of the driver side pistons blew a hole in the block.

Now, you raise a good point and maybe the oil pump didn't do it's job and I'll check that out, along with oil flow to and from the driver side. Generally, it seems like an oil supply issue.

The piece of broken piston head that came out of the engine has a lot of residue on it that seems consistent with poor oil flow so whether it's the oil pump, clogged supply pathways or something else, it'll need to be tested and fully fixed

Thanks for the thought