A competent machinist can install any kind of guides you want in a stovebolt head. Bronze guides are nice, but not really necessary. The original equipment guides are cast iron, mostly because they were, and are cheap to manufacture.
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!