Chris:

The B18 based engines were AQ110 or AQ120 and the AQ130 was the B20.The only difference between the marine and passenger car head is a small water transfer pipe that requires an extra hole to be drilled into the front of the casting and a trip to home depot to get a pipe and bushing to insert.It is an easy conversion.All of the engines I have run across have the high rpm K cam except some of the AQ110's which are set more towards torque.All electricals look the same as passenger car but are Coast Guard approved Ignition shielded units.This is a very worthwile requirement particularly if you have ever seen a boat explode from fuel vapors in the hold.The parts supply for both engines is getting a little thin but most if not all of it is still available if you can find a dealer willing to help.As one of the other posts noted though they are a bit "pricey".If you are still interested,contact Tony at Verrigni Marine at 800-888-6586 as he is one of the few dealers that will take the time to seek out the old parts.Most of them don't want to talk to you if your powerplant is over 4 years old.

hope this helps

Scott