Johnny, you will have to make the call which ever way you feel is right for you and your car, The original oil used was 20 or 30 weight not multigrade. I have been told by old timers that worked on these engines back in the 50s to be careful and not to use too heavy a grade of oil, that the low pressure engines caused some owners to use too heavy a grade oil thinking it would raise the oil pressure. less viscous oil flows better under a low pressure situation. I remember seeing lots of nasty sludge in these old engines, and I would therefore certainly use a good quality H.D. (high detergent oil) as to the gear boxes I use what I can find that is as close as possible to what the book suggests.
Engine oil:
Service MS or Service MS DG Service MS for severe start and stop service during cold winter minths.
Rear axle S.A.E. weight multipurpose,(MINERAL OIL gear lubricants must NOT be used in hypoid rear axels.)
Transmission:
powerglide ATF type A,
Manual transmission S.A.E. 90 Transmission or "Multi Purpose"
