The only parts unique to the 261 are the pistons, connecting rods, and the cylinder head. Virtually anything else interchanges with the 235. The high compression "848" head for the 235 can be used on a 261 by drilling six small holes in the right place. The later model 261s (59-63) have the capability to run a full flow oil filter- - - - -which is a huge leap backwards in actually getting the small particles strained out of the oil. Start your rebuild parts search on Ebay- - - -there are thousands of suitable parts available there, and they don't get the price bump the resto-ripoff parts guys charge!
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!