Can small block oil pump be replaced without pulling the engine?

I imagine that /6 vs V8 would also change that operation substantially. OP has a magnum V8.

My car’s a bit of a special deal, there’s no way the 340/T56 will come out the top with that road race pan. When I put the engine in from the top I couldn’t even have the flywheel attached because of the combination of that oil pan and spool mount K-frame, it has to go straight down with no angle at all. Only way the engine/transmission comes out together is out the bottom on my car.

So yeah, the difficulty level of pulling the engine or doing it from the bottom will depend a lot on what components and aftermarket parts are used.
Yeah, that's a bit of labor right there. On anything that will come out the top though, I would normally get the engine out.