first, welcome aboard
is your 1985 a left over 1984 stringer or a cobra unit? by 1985, OMC was only using the 3.0. they have 140 on the valve cover
what year is the 3.0 from the mercruiser? if the 3.0 is 1990 or older, you can strip off the manifold and plumbing off the "mercruiser" down to...