There are thousands and thousands of CAT engines, that new rods and mains are installed and never plastigauged (unless there was a known problem to begin with).{this is why verifying part numbers, is even more critical}

Yes, you would need to lightly lift the crankshaft, to push crank up into the upper half of the main bearing shell, for plastigauge.

Your part numbers are definitely going to change, so get that CAT parts guy, to print out the "NPR" list = should show you, your old part number and what the "newer" part number is that replaced it. This way you don't just end up with a bag of parts, and can't really verify, if the part numbers, in the sack are correct, or not.

Personally, I'm a lot more concerned about smaller gas engines, for plastigauge use, then I am using CAT parts, on bigger diesel engines.