Perhaps the center of lift (on plane) is too far from the CG. The motor you have on there is 418lbs. I'm pretty sure the old 2-strokes that came with this boat were around 265lbs.
Curious, how much total weight did you lose when you finished the boat with composites vs wood?
Consider using a 50lb weight (dumbell). Start in the back and keep moving it forward (using no trim tab trim). Make each run from a dead stop in calm conditions. If that doesn't work, use a human. I'm hoping that moving your CG forward will help with your problem, you just need to find the magic number and weight.
Could also be a good excuse to get a trolling motor and batteries installed in the front!
BTW, you did a great job. The boat is beautiful. I will be starting on my '73 resto soon and was hoping to contact you with questions...
Please keep us posted on your porpoising solution. Good luck.
