Ok... I've had a look at all the photos you've posted (both this thread and the other) and I'm having a bit of a guess on the era.. The drive is definitely an MC-1, it has gimbal senders and the upper has a squared off 'tail'. That puts it in the early 80s.
The engine is of no help whatsoever, because it's nothing remotely like original, but some things do fit with the 80s era. Mechanical fuel pump, edge bolts on the rocker cover and centre riser exhaust manifolds...
Given that I am in the right ball-park, I can guide you to the right manuals... (I hope)....
Engine (manual #3) ->
https://docs.google.com/open?id=0B1TAvwZ3Tjhfdk9PRXBWWExTU084dXpoTUhqRk9vZw
Drive (manual #4) ->
https://docs.google.com/leaf?id=0B1...ODAxOS00YWZjLWFmZDgtZjMxNjQxOTkzMzUz&hl=en_GB
These are the genuine article (not seloc or clymer!!

), so download and SAVE them....
As for replacing with marine parts, the carb I'd put on is an Edlebrock 1409 (available from, apart from other places, Summitracing), and I'd look around for a cast iron intake manifold, that ali one won't last a season in seawater... I'd just put fittings on the bottom of the exhaust manifolds, and I'd use a late (mid 90s) model thermostat housing... Merc changed the design and the new ones use way less hoses and actually work better.... Starters and alternators, try
http://www.dbelectrical.com/ ... I'd also look at putting an electric fuel pump (with the appropriate switches ect..) Also while you up to your armpits, put an alarm on the oil pressure and coolant temp... (Have a search around here and you'll find I've recommended it to a few people, included all the part numbers you need)
I hope this can help you....
Chris.....