I think the ratio was increased only due to the 848 head being used was it not? I have a chance to get three 261 full engines from a guy. I already have a 56-57 261 block cleaned up and checked for cracks for a rebuild but if the 60's blocks are better i could always take this opportunity to change over before the machine work is done. Having a fully filtered oil system is not a priority to me. (or should it be ?)
The 261 did not use an 848 235 head from the factory.
You can use a 56-62 3836848 on any 261, but you have to drill 6 holes in the head to match up to the 6 additional coolant passages used on all 261s. Those 6 holes should be in the correct location and at a specific angle (someone posted the drilling angle for the extra coolant passages on the head - maybe someone will post a link to the thread).
Some people have speculated on how/why the compression ratio changed in later 261s - maybe someone will post information and documentation?
The full-flow filter is nice, but it might not a "selling point" in choosing between 261 year-engines. There is however the "cool factor" of having an original full-flow system with original canister. This 261 full-flow oil filtration system was the first GM factory full-flow oil filtration system (GMC did not have a 6-cylinder full-flow oil filtration system during these years).
