Chip,
there is a procedure for using plastigage on the mains, with the engine in place. What you have to do is use a jack to push up on the crankshaft slightly to take the weight off the bearings. This is mentioned in either the GMC or the Chev manual. I don't think that there is going to be a change in clearance that soon, unless there is visible obvious damage.
I had a look at your pictures and they are nice and clear. However, I don't understand where all the damage is. Are there chipped teeth in the photos, or what? If the gear is damaged, you will need to look at the cam gear too.
