go to a Napa or carquest, and tell them your working on a 1999 ( whatever boat had this 350 Vortech ) tell them it is a boat, they can usally figure that kind of stuff out for you, the closer to the water you get with your parts stores, the more probable they will be able help you, it will become. not like it's a Mercruiser 3.7L " 488 " 4cyl, where the water pump is part of the timing chain cover, my dad went thru that ordeal, ended up having a boat shop put it back togther.

it seems to me like it would be the same as the last chevy truck vortech 350, which would be 1998, I'v heard some commercial vans had them until 2000 tho.