Many if the car .12's will work but they need some work to run as well as the NR marine 12. I've used at ton of them. The best 2 I have used are the Picco JLR Red dot on road and the OS TZ12. I don't think the TZ is available anymore though. Both of those engines will do well if you raise the liner 0.030, machine down the head button that same 0.030, set the head clearance at 0.006-0.008 and run a TZ18 carb or a K&B black carb. THey tend to use turbo plus which are expensive and they eat plugs like tic-tacs. Actually either one of those engines will run will in a boat stock. Just get the head clearance down and and cut down the cooling fins. They like to get hot.
I think the high end NR on onroad engines may work well right from the box. I think they have higher timing than many of the others.
Believe it or not, one of the funnest boats I've owned was a Wildthing12 with a TZ12 in it. I'm working on another on right now actually.. going to try a RB engine in this one..