The crankshaft snout should measure 1.125", and the balancer hub should have an ID about .002" or so smaller than the crank snout. If the keyway isn't worn where the balancer can rotate back and forth, just drill and tap the crankshaft snout for the same 7/16-20 center bolt and washer that's used on the 1970-up small block V8 engine. A worn key slot in the balancer requires a new balancer, or another key slot can be broached in the old one. A worn Woodruff key slot in the crankshaft can be welded and re-cut by a good machine shop, but it's an expensive fix that requires a full teardown of the engine.
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!