...I prepped, primed and painted my block after installing a new head gasket, water pump and t-stat/housing this weekend in my AMC 258. I flipped it over to replace the main seal and install the pan and found a nice scratch all the way around the main bearing. I pulled one rod cap and found the same damage.

I can see the crank journals have the finest ridges but no scratches corresponding to the scratches in the bearing. Is it possible to have damaged bearings but the crank be fine?

Is it stupid to wash the block and cranks and install new bearings and go?

The bearing material should be softer than the crank so it is likely they would show damage before the crank. Odds are Whatever caused the damage has likely gone through the motor and is either in the pan or the filter. Since you had the head off I assume the bores show no damage, so the only other place to look would be the cam bearings and valve train.

Depending on how big a risk taker you are, you can put new bearings in and hope for the best or tear it down to look for damage or junk elsewhere. Clean out everything including the oil passages, check the cam bearings, timing gears etc and reassemble.