The receipts for all the bottom end work done in the 70's indicated that the big con-rod ends were checked and serviced, and in my rush to attack the sludge trap I neglected to take any measurements. For shits and giggles I figured I'd check at the minimum the side clearance since it's the easiest to measure. Can't get any more middle of the road to spec (0.3mm-0.5mm) than that.
Also tried one more thing to free the oil drain plug on the sump before drilling it out. Thought outside of the box for once and put the plug in a vice, then used my body leverage to turn the pan instead of the rounded out plug. Immediate results.
Now I'll have to find a replacement plug (or make my own). Going to turn it into a magnetic one using this idea from ThisOldTractor.com. What a great resource that site has been.