The external dimensions on the 235 and the 261 are identical. They just recored the block to handle the bigger bore size. One of our competitors in the "hobby stock" class on the round track circuit in the early 1960's ran a 261 in a 50 Chevy business coupe against our 239 cubic inch flathead Fords in 46 Ford coupes. He claimed it was a 235. He gave us quite a run for our money until we put in Mercury 4" stroke crankshafts and got the cubic inches up to where we were competitive again. When one guy cheats, everybody else has to follow suit!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!