The only major differences in the 235 and 261 is the bore size- - - -3 3/4" instead of 3 9/16". The crankshaft and other internal parts are the same as the 235. The cylinder head has extra holes in it to allow for coolant flow past the "siamesed" cylinders- - -no gaps between them, but a 235 head can be used by drilling some small holes, using the 261 head gasket as a drilling template. The hot setup is an "848" cylinder head (last 3 numbers of the casting code) off a late-model 235, with higher compression. The later-model 261's can also be set up for full-flow oil filtering, another plus to using that engine. It takes a pretty knowledgeable observer to see the differences in appearance in the 235 and the 261, so you end up with a sort of "sleeper", more performance than a first glance indicates.
Jerry
