Most unusual - I've taken apart many 235s and 261s, even one that that had sat for over forty years, and have never had a pump body that did not come out fairly easily. It was certainly intended to be serviceable. However, it could be serviced still in the block, as CNC-Dude mentions. One of my 261s has a GMC oil pump. Based on the gear size, the GMC pump should pump about 10% more oil than a Chevy pump. Tom Langdon says that there is no real need for the extra pressure or volume, however. I'm using it just because of the link to the glory days of the Chevy six.
