No problem using the Diesel-rated oil- - - -if it's rated for engines with 22:1 compression, handling bearing loading on a 6:1 engine is as piece of cake!
Up there in the great frozen north, you might consider one of the heavier viscosity multi-weights for better flow during cold starts, the above 15W-40 or maybe a 20W-50. My objection to the lightweight stuff is that it's intended for modern engines with microscopic oil clearances, not the gaps you could throw a cat through on old stovebolts. Something has to be there to cushion the parts as they try to hammer each other, and slightly thicker oil is the logical choice.
Here's another experiment to try in the interest of proving my point- - - - -lay a piece of cotton denim on a concrete floor, then fall forward and do a face-plant onto it. Now do the same thing, but substitute a sofa cushion for the denim. Same material- - - -cotton- - - -different thickness! Now do it again- - - -and again- - - - -and again- - - - -66 times a second. That's what rod bearings are doing at 2,000 RPM. Tell me which one you prefer, for running a few thousand miles between shim adjustment of those Babbit rods.
Jerry
