Re: 56' Seahorse 30 needs parts
they're still around. placing a free classified ad at aomci.org is your best bet for a set of used lower unit gears or even better, a whole used lower unit. The askamember section is awesome,too. ebay can sometimes be a good source for parts but I'd trust the aomci members to take care of me much more than an "ebayer".. laings.outboards is one of my favorite sources and the guy that answers the phone is helpful, knowledgeable, and responsible. ships fast unless parts on backorder. I don't have a parts list for a '56 30hp., myself.
Seaway marine on the internet I hear is good, too for parts but I've never used them.
Original repro. decals, tiller grips, and some other parts for good buying or just lurking is nymarine.ca who also has original paint colors which are high but worth it. The guy there is reliable and helpful, too. Iboats has coils and such for your motor for a reasonable price.
--I hope you're using 24:1 fuel/oil mix!

Nice motor!
JBJ