gonna rebuild my Pontiac W72 400cu in motor, thinking...(danger/warning/etc.,) anyway, how 'bout "break in" on the Mobil dino/Chevron dino Diesel oils?? (Delvac/Delo I believe) for 500 miles, change it w/ filter and then again another 1000 miles oil/filter THEN switch to M1? (15W-50 or 10w-30)?? Is diesel oil ok for gas engine "break in"? this is circa 1976~ technology engine so I thought the 15W-40 would be correct viscosity, motor will never see below 40'F , rarely below 50'F, just as rare over 90'F but, might be "driven a bit hard" after break in..inputs please!