Changes were made to the crankshaft.
Early 12mm, later 13mm.

Very early 3.5's sleeves had a smaller O.D. Crankcase I.D. and sleeve OD must be checked.
Early size is .750 -- Late/current size .765

Early inboards and outboards were equipped with an exhaust throttle and venturi, no carburetor. Rather difficult to adjust and set up. We suggest converting to a carburetor.

Early outboards, 8906 8383... Lower leg has short skeg and a clamped in prop shaft housing assembly.
New style left had threaded prop shaft housing will not fit. You must replace the entire lower unit.
Some of the first PTO plates only had one ball bearing, usually if the square drive side is worn you will leak crankcase pressure and engine will run poorly. First PTO has a lock ring pressed on the square drive side which was eliminated in the late 1980's.

Head squish band clearance .018 (18 thousands)