My late 261 (3769717 casting number) has the head casting number 3836848 on the intake side - but also has these numbers like this on the opposite side:
B40 848
850
When I get this head removed I will CC the combustion chamber and compare it to a 235 "848" head - but I'm pretty sure it will be the same. This head will give lower compression on a 261 due to the larger bore size. Corvette motors used yet another head (3836241) but I think it was basically the same except the casting was different for the unique Corvette water pump.
We have data from original GM blueprints that lists chamber volumes on some of these heads. It will appear in the 12 Port News soon. Any confirmed info on the Canadian heads will be included if someone can provide it.
