235 heads will bolt up to the 261 blocks,BUT,the the 261's have a few more steam ports. If you take a 235 head as a replacement on a 261,the extra steam holes NEED to be drilled to match the 261 block. easy way: order a 261 head gasket,(a MUST),lay it on your "new" head,then scribe and drill your steam holes. There is some discrepancy,on the "Big bolt" forums, about whether or not these holes need to be drilled at a precise angle,or not. One more note of interest for all of us that run solid lifters: we NEED to use zinc additive in our oil, since the new formulated oils eliminated most of that additive,thanks to the E.P.A. I'm NOT selling anything here,just following advice given by Patrick's antique cars and trucks. You may call them at:(520)836-1117, for more info. Just trying to keep our engines in good running order. THANKS!!
