Mercruiser used many engines, though usually GM based. When most folks hear "Mercruiser", they think of the 3.0/181 and derivatives of the Chevy ll/ Iron Duke. Mercruiser also used the 4.3 Chevy V6 as well as 305 and 350/5.7 small blocks. The Mercruiser 470 is a different animal; an "in-house" purpose built marine engine manufactured by Kiekhaefer Mercury that is a 4 cylinder 3.7 liter (huge for a 4 cyl!) alloy block with Ford 460 head. The back of the block is the Chevy pattern, so any V8/V6 (90 degree V) bellhousing bolts up. The rear of the crankshaft may or may not be bored for a pilot bushing, and flywheels can be a Ford or a Chevy part number. My earlier post touches on some other peculiarities. As with any engine conversion, there will be lots of fabrication. I have one of these engines set aside with hopes of using in an FC150 because of unique space issues and the ability of bolting up an automatic to the 470 engine. FC's have crazy remote shift linkage that is less than ideal, so a cable controlled automatic has advantages.