I advise to see if wearing right prop 1st, then if OB is mounted properly for that prop 2nd ... before you try other things 3rd.
PROP - Check your prop diameter and pitch, for that exact motor and hull (and load/gear routinely carried), here: https://forum.tinboats.net/viewtopic.php?f=4&t=37433 If your hull is not listed, find a suitable alternate make that fits your specs.
HEIGHT - This is arguably the BEST post (IMHO) ever written on checking and confirming OB mount height - https://www.veradoclub.com/index.php?topic=137.0
HULL - You could have a 'rocker' in the hull that is causing that porpoising. You have ample motor HP, so the LU angle is trying to keep the bow up and lifted, but it's not enough. Some of that can be caused by the wrong prop, some by the hull. As otherwise I'd opine (thru cyberspace review anyway ... ) that your mounting height looks good.
HOOKS & ROCKERS (from iboats) - When viewed from underneath the boat, looking up at the bottom, a hook is a concave deformation of the bottom along the keel line. If the deformation is convex in shape then it is called a rocker. If you put a straight edge of about 6' in length along the keel line, from the transom going forward, you will easily see if you have a hook or a rocker in your hull.
A hook will cause the bow to dig in the water when you're on plane until you add excessive trim - at which time the hull usually starts porpoising. A rocker will porpoise most of the time at any trim setting and the boat will handle very weirdly. Sounds like your situation :?: ? Both hooks and rockers are usually spread over a 2-4' region just in front of the transom. They should not be confused with shapes/transitions that the hull designer may have added as a design feature.
The photo attached was from a recent post where I showed someone else how to confirm that they had a 'hook' in their hull.
DH Note - I believe that either could be created onto a tin hull by an improperly setup trailer (bunks, rollers and/or their positions (fore/aft or side-to-side) with heavy road use, damage, too heavy hull loading, or impact or just age and settling on an old aluminum boat ...