Steve, the diagnostic makes sense. I'll try that today definitely.

I did check the needle and seat in my carb when I took it apart. It, and the floats, looked alright. I suspect that when I put the Edelbrock carb onto the car, it'll run. Maybe rich, but it will still run.

If so, I will just have to look more into whether it's a fuel pressure problem (can fix with a regulator), or a carb adjustment or float issue. It makes sense that it's doing this, because now that I think about it, I checked the floats before I ran the engine and set them perfectly, then right after I checked them again and fuel poured out of the sight plug when I opened it.

I will also definitely do an oil change. It is almost time anyway, plus I want to take off the Fram filter that I used for break-in (had it lying around, so it was free).

My next question would be - what made the car run fine for four hours, but then suddenly gain this issue while I was idling?