The truck is a mixmaster anyway, not some pristine trailer queen that's going to win points for originality at a concours show somewhere. Find a good-running 235, or at least a rebuildable core, and do the small modifications necessary to make it fit. If a 261 is available, nothing beats a few more cubic inches, particularly in a truck that still works for a living.
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!