There is difference in a marine Vs automotive. First of all marine blocks are 4 bolt mains, added piston to wall clearance, more than likely big port heads depending on hp rating 330 and up are the big ports, and they also have different cam grinds. they will use oil in a street application do to the added clearance. In a marine engine the block stay's much cooler than in a automotive application and the piston stays much hotter. That's why they and the extra clearance. Marine engines are set up to run at higher sustained loads at 3000 to 4800 rpm's at over 50% throttle and up to wot for long periods. Also cast with a higher nickle content.