The D3 heads are the standard issue for 460 engines in boats. 91cc quench chambers, 2.09" intake- 1.65" exhaust. With those heads on a 73 & up block [10.320 deck] is 8 to 1 C/R. Switch to an earlier head [stay far away from the D2 heads-junk open chamber] like the C8-C9 or D0VE heads, they are 75 cc chambers with the same size valves. That would boost your C/R to about 9.5 to 1, clean out the restrictive exhaust port and do a 3 angle valve job. Get a cam from any one of the well known cam companys, let them recommend a grind for you. Install a good aluminum intake like a Stealth or a Victor if you want to run a single plane manifold. Don't run any carb smaller than a 750 cfm, preferrably a 850 cfm as BBFs like airflow. The big Ford also responds good to headers but I get the impresson you want to keep the transom exhaust. You will need to see to it the carb gets enough fuel so a good fuel pump and big lines are mandatory.