What cam do you have in the car? mechanical or roller? if mechanical then go with Gibbs' (my favorite) or Brad Penns' because they have the lead/zinc additves for mechanical cams; if you have modern roller put whatever tickles your fancy, 50w sounds ok to me if you have carburated motor but if you have modern injected motor the heavy weight oil may squew the temps and the 'putor might do some odd stuff - i am not sayin that it will, it is just a thought.