As far as I can tell, the steam holes someone drilled in the 235 head go into a water jacket. They're not blind holes. The block lacks some large water holes between cylinder 1&2 and 4&5 on the push-rod side that the 235 gasket makes provision for. As HRL has said, that may force water through the "steam holes". The gasket not having steam holes doesn't seem good to me in light of the lack of the big holes in the 261 block. So all in all, I would say that it's necessary to drill the 235 head when used on a 261 block. And also NOT to use a 235 head gasket on a 261, even though it'll fit.
My 261 did come with a Rochester B on it but no tag number or other ID. I'll probably use the dual Zenith 228 setup off the other engine. They have adjustable main jets. But I wonder if I can safely drill out the vacuum port in the Offy manifold to take a 3/4 pipe fitting. It presently is drilled for 1/4 pipe. I need the big fitting to take the PCV and brake vacuum connections.
I took the PCV Valve off yesterday and checked that the gizmo inside is free to move. On another 235 with a road-draft tube, when it began throwing oil out of the tube I popped the top off the mist condenser and found the oil return holes were completely plugged. I took a torch and burned out the residue, which cleared out the little holes, popped the top back on with some RTV and that fixed the problem. Perhaps that's what's wrong with this one. I'll look.
