Abstract: An adapter for interconnecting a marine engine to a stern drive includes an adapter ring having a pair of concentric flanges with bolt-receiving apertures formed in each of the flanges. The outermost flange is secured to the flywheel end of the engine. A coupler housing is secured to the flywheel end of the engine radially inwardly of the innermost flange of the adapter ring and houses a coupler having an internally splined rotatable part, and a bell housing having a radially outwardly extending flange is secured to the innermost flange of the adapter ring in housing relation to the coupler housing. A trailing end of the bell housing is secured to a transom housing which is centrally apertured to admit an externally splined stern drive rod to engage the rotatable, internally splined part of the coupler.