You can use 30W in your engine, but I use Valvoline 50W ZR1 racing oil, since it has zinc additives which should lubricate our flat tappet camshafts. If your engine is old and not rebuilt there could be a problem using a detergent oil which might flush deposits out of your engine and clog your filter (like it is supposed to do) You might want to find some non detergent oil in this case. Bonne chance!
Ron, I use GOOD 20W-50 IN MY 1929 14l and also in my 31 22A. There is a version with the proper additives and Zinc Called Castrol GTX Classic 20-50 engine oil. You can get either the 5 quart jug or six quart bottles.