That rocker arm bushing setup wouldn't be difficult to duplicate with a tool post grinder and a couple of chucking reamers, as long as a bolter has a lathe and a little bit of machining experience. Grind the rocker shaft down a few thousandths to smooth up any wear, ream the rockers slightly oversize, and press the bushings in. Tooling up to make the first set would be a little pricey, but the cost could be amortized by selling the re-bushed assemblies on an exchange basis, similar to what starter and generator rebuilders do.
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!