Hy Guys, I just happen to be rebuilding a Pontiac 261 at the moment and I'll try and answer the questions that have come up.
The clutch housings are different between the Pontiac and truck 261s, but only as it pertains to the application, the housings can be interchanged.
The 848 head on this engine does have the extra cooling passages drilled
The particular Pontiac 261 I'm working on did have the bypass oil filtering system, I have converted the block to full flow filtration. My particular Pontiac 261 is a 1957 model so I cannot speak to whether or not the 58-62 Pontiac 261s had full flow filtration, but I don't think they did, hope that helps.
