Chris Craft Lancer 19

I just purchased my first fiberglass project boat - 1970 Chris Craft Lancer 19ft, Chevy 307 v8, volvo 270 outdrive.
The engine has water in the oil, so I know it is going to need either some work, or replacement, which I am more than able to do myself - not overly worried about that part. What I am curious about is the hull speed of this boat, and perhaps what the optimum horsepower should be to get the best speed out of the hull without sacrificing economy too much. I already know that there is a balance here between the two, and hp/speed costs money, but I'm just not familiar yet with this hull and what would work best for cruising. I have heard that the Volvo 270 outdrive will handle up to a 350 cu/inch engine, but that isnt the whole story, as it is really torque and horsepower that is made by the engine, and a 350 can come in quite a few variations from mild to wild. I believe the 307 is just over 200hp and probably ok, but would a few more hp ( maybe250 - 275 ) be worthwhile and not wasted effort?
Thanks in advance for any help with this boat. David