what do you recommend as timing ? 35 at 3000 ?

Timing is very much a specific situtational requirement.

Guided by rules, not always firm.

WOT: Unless you have fast burn chambers and high port swirl, you need at least 31-32° adv. Very rarely would you go over 36°

Load Load and High Vacuum: timing can be really high... 46° area. Lean A/F mixtures need more time to burn. High vacuum from minimal throttle opening, crrates a very low dynamic compression. The lower pressure slows the burn down. Needs more timing.

Mechanical distributors were never able to account for low load advance. Vaccum adv distributors were able to help out, and the engine becomes more efficient.

Typically, marine engines want to good timing under load, certainly under acceleration. Light planing cruise, there may be some room to increase timing, but the risk is higher.

Essentially, 34-36° adv timing timing is the ballpark area. SBC/BBC. Vortec chambers will generally want less.

If your compression is too high on a marine engine...and you've retarded the ingnition to account for it, (29-30° area), the peak cyl pressures are not at the optimal crank angle, and the fuel is burning more than you want as it's blown past the exh valve/port. This creates a hotter than normal exh valve, and adds detonation issues.