Didn't most of the school buses in the late 50's/early 60's run 261's? You might try looking for abandoned buses that are being used as storage as a possible source, if there's still an engine in place. Several salvage yards in the rural Tennessee area used to buy up retired buses and store parts in them. Chances are anything like that has been scavenged or scrapped long ago, but it's worth a quick checkout if you see one 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!