They were called additional coolant passages by GM/Chevrolet. I get worried when I hear about steam in an engines cooling system - if you have steam, you have problems.
Jim Carter is the source of the "steam holes" misnomer.
Matt,
It looks like you will just have to take your chances with the 261 head gasket. If you use the 235 gasket, there is no doubt you will block those additional 261 coolant passages.
Let us know how this works out.
