I have not done such a conversation, but I think after you solve the usual
engine marinization issues, the transmission becomes an issue in my mind. I
would be concerned about it's reliability in constant heavy load duty. If
this is a mud boat for the duck camp? then it's a good fit as it's loaded
running would be short? But if this is to be run 1,2or3 hours fully loaded
,then you could run into some trouble. It comes out of a intermittent load
duty, air cooled (with plenty air flow) duty, You would be putting it in a
constant heavy load little or no air flow. So more lots more load duty with
less cooling. If that were the case and you didn't want to find a marine
transmission I would think it needs it's own cooler with a circulation pump
at a minimum.

--
Ron White
Boat building web address is
www.concentric.net/~knotreel