Read a lot of info here wrt oil. I have been running diesel 15W40 with ZDDPlus but seems like the majority feel diesel oil is not the way to go with the detergents in it. VR1 seems like a good choice but can I just switch from 15W40 to the 10W30 VR1? Is the 20W50 VR1 too thick? 1969 426, stock, solid lift cam. Thanks.