1955 235 engines are factory HP rated at either 3800 or 4200 RPM, depending on the specific application. Any speed below those numbers will be "safe" for a good condition engine with proper connecting rod bearing clearance. Very few stovebolters ever rev their engines that fast, so "safe" rpm suggestions are usually a solution in search of a problem.
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!