Been working on a lot of Chevy small blocks lately. Chris Craft began converting sbc's for marine use at the tail end of the '50s, and did a lot of interesting things with them. Depending on the needs of the hull, they were mounted both backwards and forwards, and were built in both regular and reverse rotation configurations.
A 327 in an 18ft runabout has some serious ass, especially in a 70 year old wood boat. It's impressive how quick these are.
For the traditional F motors (like the one in pic related), the major marinization changes generally consist of:
>new oil pan and sump (because of the mounting angle)
>marine exhaust manifolds
>raw water pump driven off a gearset at the back of the motor by the transmission >new crank so the flywheel can mounted on the front
>additional oiling passages for the trans since it shares engine oil
>marine carbs that lightly spring pre-load the float to keep them from bouncing in the bowl through wake
And a bunch of other smaller things. It's been very interesting learning about these old car-turned-boat motors.