If it's been in reasonably dry storage, a 261 block without all the other parts is worth a C-note or slightly more. The crankshaft and rods will swap with a 235, so the siamesed-cylinder block with the 3 3/4" bore and the pistons are the scarce items. Pistons are available new, in various oversizes in case it needs a rebore. Blocks aren't. Offer him what you think the block is worth, and scrap metal price for the rest of the pieces.
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!