CNC-Dude, I'm well aware of the "steam holes" between the siamesed bores as one among a few defining features of a 261 engine. As my original post states, there is a noticeable difference two different 261 head gaskets, one typically made by Fel-Pro and one made Best. If you review the attached images in the post (one displays, the other seems you have to click on to load) you will see the difference I mention. Basically the Best Gasket covers some of the holes on the front side of the engine while the Fel-Pro one does not. Again, the only thing I can seem to guess is the Fel-Pro one may be based on the gasket used in 1954 (I base this on finding a few NOS 261 gaskets listed as 1954 only), when the 261 was introduced, but they adjusted the gasket from 1955/1956 onward maybe on account of some minor heating issues at the rear of the block. My question was, if my assumption is right as I can't see any literature or discussion on this topic.
