James,
That is very cool that you have your grandfather's GMC. I hope my grandson adopts my '36 Chevy pickup someday. It's unlikely that I'll be around to see that '36 turn 100 years old but my sons and grandkids should be able to.
Since you're so far into the engine disassembly it might be worthwhile to you to inspect the condition of rod and main bearings and crankshaft. If there are any problems those components are accessible now.
Is there any rust damage in the cylinder walls?
Have fun!
