For what it costs to rebuild any motor these days, I wouldn't use any oil not made for older engines or any oil not designed for flat tappet engines. If you want to run oil made for diesels, thats up to you, I prefer race oils or muscle car oils. VR-1, Driven, or Lucas would be a good choice and 10-30 would be what I would run. Camshafts lobes get 90% of their oil from what the crankshaft throws at them, the thicker the oil, the less is thrown. I build Pontiac engines for local restoration guys, my oil choice is Penn Grade 30w break-in, then 10w30 Penn Grade. They have the required additive packages made for gas engines, and at $5000 - $6000 per engine, I not willing to test my luck with just any oil. The break-in oil was $59 for 6 quarts, to me thats well worth it, it hasn't failed me yet. Two years ago I built a 400, broke-in with Penn Grade, drove the car around for a couple days and delivered it. Three weeks later I get a call, engine misfiring. He brings it back, I pull the rocker covers and find damage to pushrods. With a complete tear down I find the cam went flat and took 6 lifters with it. $1000 later it back on the road. He told me he changed oil right before it messes up, he bought Wal-mart brand oil, 10-40, no additives. He had about 15 minutes drive time after the oil change before the cam went out.
My 1970 250 has 10w20 full synthetic in it.
Thats my opinion, take it as you want.
