Just think of everything at back of your 235 as a unit, bellhousing, flywheel, starter, clutch etc, if in good shape can all be left as is when slipping in the new motor. I went with a 261 in my 46 pickup, still using ALL the '46 components, even the foot starter.
Use your 261 head gasket as a guide to drill those steam holes, easy deal. Also with the 261, my 1961 year motor has one 'bastard' head bolt that is drilled to allow oil to top for rockers, it's center bolt on distributor side, don't lose this bolt. Not all years of 261 have this drilled bolt, just be sure you have oil going to top end.
Best of luck
Jim
