Your "machinist" sounds like a doofus who shouldn't be trusted with anything remotely related to automotive machining! According to my Federal-Mogul shop specifications manual, all of the GMC inline sixes have the same rod and main bearing sizes and use the same bearing part numbers:

Rod bearigngs : Federal Mogul 1905CP
TRW CB427P

Main bearings: F/M 679M
TRW M929P

Connecting rod journal standard diameter: 2.3110"-2.3120"

Main bearing standard diameter:
#1: 2.6835-2.6845
#2: 2.7145-2.7155
#3: 2.7455-2.7465
#4: 2.7765-2.7775

228 Std. bore: 3.563"
228 stroke: 3.813"

I'd strongly recommend finding another shop- - - -if he screws up the block or the crankshaft by grinding or boring them incorrectly, you'll have a hard time finding a replacement!
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!