The "steam" holes are needed because the 261 cylinders are "siamesed", no coolant passages between them. The holes allow coolant to flow upwards past the joined cylinder walls instead of creating "steam pockets" caused by lack of coolant flow. If you run a 235 head on a 261, they need to be there. The 261 head can fit the 235 with no problems- - - -the holes don't have to be plugged. If you choose to use a 261 head gasket for a drill guide, be aware that the holes have to be drilled at a slight angle, not square with the head surface. I think there's a good tech tip somewhere that explains the procedure in detail.
Jerry
Last edited by Hotrod Lincoln; 10/16/2009 9:07 PM.
