Tom-
Once again your boat and work looks terrific! And you did this all in a tent during the winter?
My Seafari has more weight forward than yours. Another difference is I am running a 5 blade prop and using a Dolphin. When I raised my ETEC to 2 3/8” from keel to bottom of AV plate (about ¾” higher than the last position), the primary objective was to dial in the WOT RPM better, which I did and picked up about 1 MPH and easier steering at higher trim settings. I haven’t run the boat much since that time, but noticed maybe a tendency to porpoise at one condition where a throttle or trim change eliminated it. So at this point I am happy with the change, but even though I increased the transom 2”, I left room to put it back down another hole if needed. My operation is on relatively smooth SC lakes, not sure how it would be in the rough stuff. (As I previously remarked think I am about where Frank Brown, Moesly’s race mechanic set up my original Merc).
The photos show the back tape on my AV plate (parallel to the keel) at 0 degree trim and 30 MPH.
I don’t recall if this boat is new to you or if you used it before your project. Is the porpoising a new problem? See my example of Estimating CG shift of 9-24-16. Your removal of the casting platform and smaller fuel tank probably reduced forward weight. And did you increase aft weight? As mentioned by others a 4B prop will help lift the stern.