Not necessarily- - - - -it would depend on how much clearance the connecting rods have. Multi-weight oils actually stay at the physical thickness of the minimum weight- - - -20W-50 flows like a 20 weight when cold (0 degrees F.), and lubricates like a 50 weight when hot. The oil doesn't "thicken"- - - -it just has better lube qualities when it's hot than a straight weight oil. Any multi-weight oil including 20-50 will be "thinner" than the 30 weight you're using now. Most 20W-50 "racing" oils are just outrageously expensive, compared to Diesel-rated 15-40. The Diesel oil also has additives that are kinder to your flat-tappet camshaft than the racing oil.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!