Marine 273 build

Hey, thats neat!...273 in a boat! A lot of your assumptions above are bang on. The "302" heads are the ticket as they have hardened exhaust seats already, and smaller chambers (to help with compression). Does marine fuel have lead still? Since you aren't worried about low RPM torque, I would think you could go with a single plane-type intake, maybe a bit on the "high rise" side for higher RPM use, as opposed to a dual plane (L)D4B style.

...or you could go with a "D-Dart" style build. If you're not familiar with them, the "D-Dart" was equipped with a factory built hi-performance racing version of the 273 putting out 275HP. It had a BIG mechanical cam (not sure if a rev.rot version is available), and 750(?) Holley carb. These were built for high RPM and good power, similar to what you would want in a boat?

Here's Dave Mape's 273 page with a bunch of info...

http://users.erols.com/dmapes/THIRD.HTM