big red,
don't push that 216 too hard. especially if it's the original engine. 70+ is way beyond what these engines were designed to perform at. if highway speeds are what you are after, look into new gearing first, then engine/tranny.
the 50, 3/4 ton, 4-speed that i drive daily doesn't see anything over the indicated 40mph (actually 45mph) but i don't drive highway or freeway with it either.
i'd say with a 216, 3 speed, you would only be able to push it slightly faster than 50mph and still run within a comfortable rpm range.
if you do decide to upgrade engine/tranny/gearing, don't forget to upgrade brakes too. not a good idea to get a lot of "go" when you don't have a lot of "whoa!".
