I have a 31 hp longtail. The motor blew up last week. I'm currently looking into options for replacement. I was wondering if you have to buy the marine replacement or just the regular vanguard replacement. Also would it be more cost efficient to buy a short block go that route.

I was going to. Does anybody know the difference between the marine 35 and the regular 35. Which would be better for the longtail

It also comes with the stainless exhaust.

That depends on what you can find first and how much you want to spend. The non-marine motor was used for years before the CDI motors came out. You will be just fine with the regular motor. That being said I would get the CDI motor because the better charging system. But thats because I like to run a lot of lights and electronics.

Save some money, buy a 35 short block (~$1300) and bolt on your heads, exhaust, carb, flywheel, etc.
Comes with all internals.