1949chev34,
For normal every day driving 30 weight would be fine. If the motor is worn out or a leaker, you could move up to a 40 weight. Non detergent is still available if you search for it but detergent is much more prevalent. My bet would be your engine has been running 30 weight detergent and this would be the best choice to stick back in it.
Multi-grades are cool, but for your '49, it makes little economic sense and the old engine might go on strike with the fancy stuff.
Stuart
