Echoing the above. DO NOT USE AN AUTOMOTIVE CARBURETOR. If you feel like you must replace it, the correct carb is Holley list # 80319-1. It's available from Summit Racing for for few bucks cheaper than skidim. Sounds like your idle passages may be plugged with gunk. For the $580 a new carb costs, I'd certainly try a rebuild first. The key is a complete teardown, lots of spray carb cleaner, and compressed air to blow out all the gunk in the tiny fuel and air passages in the idle circuits. If you have a local speed shop nearby, I'd ask them for a recommendation on a rebuilder and bring the carb and the correct kit to him. When you order the kit, also order TWO new carb base gaskets; one for between the intake manifold and the PCV spacer and another for between the spacer and the carb.
If a marine service facility offered to install an automotive carb on my boat, they would be fired immediately for incompetence. I can understand it when a do-it-yourselfer doesn't know any better and wants to save a few bucks on a new carb. However, I am just BLOWN AWAY that a supposed professional marine service provider would offer to stick an auto carb on your boat. They are either incompetent or simply don't care.
1992 Supra Mariah - Red
PCM 351HO 285hp - PCM 1.23:1 Transmission
OJ XMP 4 Blade CNC 13x15.5RH
"People do weird things to boats" -Unknown