Don't marine ESCs have a different style of braking? I suppose it wouldn't matter if using mechanical brakes...
And yeah, a different heatsink would be required. As far as exactly what heatsink to use, you'll probably need to mod something. Here's a decent site with some fairly cheap heatsinks:
http://www.allelectronics.com/make-a...t-Sinks/1.html
By "HV" what are you talking about? 6s? 10s?