Marine 273 build

Welcome TR - Cool to see something different and also from CT! Some of my earlier tuning jobs were CC ski boats. I did a Ford out on the lake and the locals took notice (Crystal Lake in eastern CT).
I think if you want to keep the shortblock then there's only so much you need to really sweat. First - the compression. As you notice it's hard to get compression in a short stroke, small bore engine. Normally I'd say pistons but you want to leave them alone. You have the "later" 273 open chambers - going closed will help. Milling the heck out of a set of closed will help more but brings more issues to deal with - namely intake fitment and pushrod length.
So knowing the technical limitations leads to the next two questions:
What are you capable of doing yourself?
In real dollars what can you spend for this?