Helping out a friend and want advice from the braintrust. A friend is putting a 2015MY 6.4 Hemi in their 74 Dart/Swinger. New cam and lifters as one of the lifters was jiggily after 74ishK miles. MDS was deleted as this is a 74. The cap says 0W40 and I was going to say that is probably good to stick with in something like M1 or 5W40 in whatever is cold and on sale at the parts house. Do these really need a 40wt or are they ok with a 5W30?