Rule of thumb ..from what I can still remember... lol
30cc - dual plane, longer stroke, higher vacuum and booster signal/airspeed works fine
50cc - single plane - kind of invert to above and if your convertor is too tight.
I am always in favor of trial and experimenting. I will use the 30's I have now, then try the 50's. Seems to me the 50's would give you a lot longer shot with the same cam???