Just pm me and I will do my best to send you in the right direction. Been there done that. You'll be fine. I am no expert but any means but just going by experience. You be fine. I wI'll share what I did to heads and you might have them decked to get a little more compression as you should regardless and will open the door to alternative shelf cams. Timing events etc play a huge roll. As well as get your comprehension makes it all work. Ran cast inon heads for years up to 9:5 compression for years without any issues which can open door up to more cam options. You'll be fine

You should plan on a compression test and leak down test on your motor before you decide whether to freshen up the rings, etc. Your motor could have a ton of hours on it and depending on the oil change intervals and how many hours if wide open throttle, you may have ridges in the cylinder bores. All of this will dictate whether you pull the rotating assembly out and freshen up the bottom.
Your motor is a low compression motor, which limits your cam options. You'll have to syat with low overlap and conservative duration to keep from killing cylinder pressure. You'll have to keep a wide lobe separation to keep from ending up with water in the cylinders from reversion.
Your crank is cast. Your rods are the weakest ones available for a 454 with the smallest rod bolts. Your pistons are dished cast aluminum non performance units. if your motor is in good condition, ring end gaps are in spec, no ridges in cylinders, then sure keep planning your hopup, as long as you know that your motor should not spin more than 5000 rpm, and your compression will limit a lot of the gains you desire. Also, as has been mentioned, you do not need to port match your cast iron intake. You need to throw it overboard and replace it with a better unit.
Before you decide which intake, you have to determine whether the boat will ever see saltwater. If so, you'll have to get salt-compatible intake with corrosion resistant crossover and Tstat housing.

M

Thunderbolt IV runs off straight 12v. No ballast. The amplifier box has an internal voltage regulator (IVR) for the trigger module. TBIV coils are rated at full 12v (just has 30% more windings on the primary side). It all boils down to WHAT VOLTAGE your trigger is designed to run on. Yours requires a ballast, so you run a ballast. Then, you match your coil to a ballasted system.