A quick search of Ebay turned up a large quantity of brand new generic rocker arm adjuster screws with the same dimensions as the stovebolt engines use- - - - -7/16-20 threads and a 5/16" ball end. Apparently a bunch of manufacturers used rocker adjusters with the same dimensions, so it's not particularly necessary to look for OEM Chevy adjusters to rehab a set of stovebolt rocker arms.
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!