You'll hit water long before you get the 235 bored big enough to take the 261 pistons! The only way it might work would be to bore it out big enough to accept 3.75" by .125" wall-thickness sleeves, and turn the 235 into a wet-sleeve engine. We've done that on a few race engines, notably 2.3 liter Ford 4-cylinders with 307 Chevy V-8 pistons, but it's going to be a very short-life engine. Your best bet will be to find another 261 block somewhere.
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!