That motor needs to be at 38* total timing at 3000 RPM, jets should be 88/92. That boat will spin up to 5500/5800 it just needs someone with a little patience to make it happen. With that single carb, if there's not a 2" carb spacer under that carb, I'd put one on it, I run a Wilson Manifolds 2" billet spacer, it makes a night and day difference. If I recall that carb is an 850, keep your eyes peeled for a good 950HP unit, that'll make a big difference in that motor. You may also want to run the valves, I'm not sure how long it's been since that's been done. There's more in that boat than 67 MPH. Lots more.