I'm pretty sure the M45 is a bolt-in swap. You might have to tweak the inlet and output lines a bit to make everything line up, but nothing dramatic. I don't remember exactly when Chevy swapped from an oil pump pickup screen mounted to one of the main bearing caps to one that threads directly into the pump, but I'm pretty sure the pump itself is the same. Whatever pickup is there now should be a direct swap to the new pump.

BTW, in 60+ years of building engines, I've seen exactly three "worn out" oil pumps that didn't have a catastrophic failure like ingesting a big chunk of metal or something similar. It's far more likely that you've got some badly worn bearings that are consuming more oil than the pump is able to provide. Also, try removing the pressure relief valve in the cover of the old pump and check for a piece of debris that might be holding it partially open. I've seen that on several occasions.
Jerry

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