Just use a the pointed part of a dial caliper to measure the crankshaft diameter after you get the first bearing out. You'll be able to get a close enough estimate of the diameter to figure out if it's undersize or not. There are .001" and .002" undersize bearings available to compensate for minor crankshaft wear without regrinding, IF the crank isn't worn egg-shaped. Be sure you don't create a tight spot if you use the 1 or 2 under bearings, however. I always check for proper clearance with Plastigage when I'm replacing bearings without a full teardown and regrind.
Jerry

PS: If the bearings are factory original to the engine, they probably won't have an undersize stamped on them, just a part number. That would probably mean they're standard size, but don't guess, measure!
Jerry

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