Mercury Mark 55 on  Mark 40H or 55H? tower.  This a stock Mark 55 power head with the crankcase opened up to accept KA7A carbs which are on the engine.  Partial serial number starts with 791 on the tag, we have not checked the number on the block. Has a nice prop shaft on a Mark 55H gear case, no paint on the lower pan with a red top recoil, The exhaust snoot is welded which makes us think the tower housing is a Mark 40H.  There is an extra hole drilled in the top cowl for the choke rod. Mark 50 serial tag. The stainless steel wrap is not correct for a 55H and has the altenate valleys painted black. This engine is part of the 25 engine purchase we made from Jerry Heywood.