318 marine motors?

a buddy of mine just bought a 57 CHRIS CRAFT day cruiser boat. it has twin 318's (i think) in it. they are definately s/b l.a series mopar motors. wondering if anyone knows anything about theese motors, is there any difference between them and the 318 in my van? they have a weird box behind the dist. that says chrysler electronic 225 on top with a big red reset button. other than that they look vary similar. ive heard chrysler marine motors are heavy duty versions of the car motors. not sure how true this is, any help is greatly appreciated.
cheers