The 261 did not use an 848 235 head from the factory.
This statement may confuse and does not apply to Canadians. Up here (in Alberta anyways) there is an abundance of 1955-1962 Pontiac cars which came with a 261. They all have 848 heads (drilled by GM of Canada), hydraulic lifters, bypass filtering, and a fiber timing gear and are far easier to come across than a full flow version from a truck. So far I have not found any GM of Canada documentation to support this however.
I wanted to find out definitely what was up with the "steam holes" and so cut up a head to investigate this as well as port shape and possible alterations. I see Pre 68 Dave now has that picture in his album as does Deve and who knows who else by now. The full album of the cut up head can be seen
here.
