Anything that helps you enjoy the hobby more is alright with me. I think a fat fifty cowl on a V4 is a great idea. I considered it, as well. Instead, I am putting twin 1961 Johnson 40 hp’s with 1958 Super Seahorse cowls on my 1956 Lone Star Cruisemaster. That project is a long way from done. I am curious what prop pitch you are running on your twins. I know that elevation plays a part, but 17-21 mph sounds low on an El Dorado.