[OMC-Boats] What makes a marine engine, marine?

As Lee pointed out; if you ever get the blank stare from the person at the parts store when you tell them your working on a vintage 60's boat with a 225 odd fire buick V6 (used to happen to me all the time) just back up take a deep breath, reset and request the same part for a 69 jeepster and all is well!! So JD, Lee beat me to it, rather than a skylark I tell them a 69 jeepster. (I used to have one) This brings up a question that's bugged me for a long time....

What EXACTLY makes a marine long block or short block....MARINE?

OK, so anybody that's been reading this list should know that the following are special marine parts:
carburetor/flame arrestor, altenator/voltage regulator, starter, fuel pump, water pump, the thermostat housing and exhaust manifolds are clearly application specific.....

What I am talking about is the LONG BLOCK; the block itself, crankshaft, pistons/rods, heads, valves, pushrods, timing set, etc. Is there anything special about this. In other words, is there any reason why someone couldn't buy a long block for say a 69 jeepster and bolt on all of the marine specific stuff?

I recently replaced the "long Block" in my tow vehicle (89 F-250 351 windsor w/EFI), was less hassle than tearing down the old engine, figuring out how to get all the parts to a machine shop and less expensive than a rebuild anyway. It came with a 7 year 70K mile warranty, was tested and guarenteed, they dropped it off at my door less than 36 hours after ordering it and picked up the core when I was done. This was my first engine swap and after all the smog and computer stuff, I'm thinking doing something like that with that SUPER SIMPLE little V6 should be a piece of cake, once you get access to a hoist tall enough...

Any thoughts???

Cheers,
B.C.