For 1966 they report 38, and then 36 for the last 10 built in 1967. In all, 80 inboard 20' Sea Skiffs were built. Great boat, I love it because it's a UTILITY design, but it is not a good ski boat due to the deep v, mini keel, and how an inboard of that design won't turn at high speed (at least with the rudder I have on the boat now). She wants to lay over on the chine when it comes time to do one of those high speed slingshot water ski turns.
Looking for the perfect prop, and I think I have, the boat will go "almost" that fast but not quite. I get RPM right up into the 4000 rpm range with the 13x13 RH 1" cupped I'm using now. GPS shows around 34 or 35 but I would prefer to get a hand held sports radar on it for the real check. I really had hoped for more speed than that, so I guess I'll just hold back until the motor needs some work.