Full flow oiling won't gain anything appreciable. It's really nice to have on some engines, but since an engine really doesn't create much crap in the oil for a given amount of time the filter keeps up just fine. Another perk, seeing as the filter only filters the excess pressure from the pump, it is allowed to have a finer filter, that's why a bypass filter kit is available for modern vehicles too, particularly highway trucks and such. I think Don and Merle have the oil modding thing taken care of, but like they said stock is pretty much the best formation except for super high performance. These old flatties were darn near indestructable as-is, with the addition of modern oils I could easily see one lasting well over 100k.
PS
-I think it's the chevy stovebolts that had oiling issues, those have come up a time or two on here
-Josh