I went back and found the frame to oil pan bolts that came out of the 126, in a nicely marked bag - which I couldn't find...
The bolts measure 7/8 inch long and have a single lock washer, no flat washer. They are also grade 5 bolts. All of the bolts on the 126's pan were the same length. In as much as the frame thickness doesn't change, this makes sense. I'll double check the allowance for thread length/depth before I reinstall against bottoming out the bolts into the pan too.
I pulled the head on this 122's engine and it looks very good inside. Standard bore/piston and still some cross hatching visible. What I need to replace (or at least I think I should) is the drive plate. The one on this engine is warped like someone used a pry bar on it. I've got a spare, just got to figure out how to get it loose from the engine.
Next up is to flip the engine over, replace the aluminum pan for a cast iron one, remove any balance gears if present and put back together.
I'm debating painting the engine and will likely not do so. What I need to do before I do an 85 point or less restoration is get this tractor running and working to see what I've got.
Also the clutch friction plate holes for the drive plate pins are somewhat ovaled, but no real damage that I can see, so don't know that I'll replace it for now either.
I'm impressed with how easy these 126 and 122 gear drive tractors have been as far as pulling the engine. Very simple and straight forward as compared to my 1650 and another color simple tractor I've got with a Kohler Command in it.
I appreciate everyone's help.