Most agree multigrades are just fine for almost all jobs but what about hot weather use with no cold starts on a hot small block or big block such as a 350/383 stroker, 383 Dodge, 454, 440 or 426? Should one jump right up to a 40 or 20W50 weight or would a group 4 SAE 30 (AMSOIL diesel sae30) be ok for most non drag race conditions? Also what weight of oil was used in the 60's and early 70's in such motors in cars and trucks?