As good as the engines are, the unfortunate aspect is the parts, and particularly marine accessories, are disappearing. Some are long out of production. For this reason, I'm gonna repower my 31' sport express with (probably) 383 Chevies, and current transmissions.
I've raced a 1960's VW based car in sportscar racing for years, so I understand the problems inherent with old but good stuff. Keep 'em going as long as you can, and squirrel away spare parts if you can find them.