https://www.perfprotech.com/blog/art...a2-sterndrives Histroy of the Mercruiser Alpha Sterndrive
Beginning in 1983 Mercruiser introduced the R/MR/Alpha 1 series of sterndrive models. These units differed greatly from previous years not only in design but also in that the flywheel housing on the engine changed at this point. This creates one of the big break points customers should be familiar with when inquiring about re-powering older boats. Since the flywheel housing changed from 1982 to 1983, you cannot couple a new engine to a pre-1983 sterndrive unit as the rear engine mount spacing differs on the new engine and therefore will not match to the old style inner transom plate. The other difficulty is that the newer 14 inch flywheel utilize a larger coupler that prevents re-using the old flywheel housing on the new engine.
R/MR/Alpha Generation 1 model began in 1983 and ran production through 1990. The
Serial Number Range for these models ranged from 6225577 Thru 0D469858
