Not familiar with the boat. You are on the right track to solving your problem. Usually porpoising is the thrust of the prop is (exaggerating) trying to push water up in the air, making the bow (front) of the boat rise. Solution is either speed up till it quits (available hp limits that ability) or tuck the lower unit in closer to the boat so that the prop is trying to push water deeper. If you are running a side console or tiller from the rear seat, you need to do as you have done and move things forward since you said you are tucked in as far as you can go and you only have so much hp. Last, problem may be caused by the hull having a hook or other variation caused by sitting too long on a trailer out in the elements. That pretty much can't be fixed. If nothing else fixes it, get a Whale's Tail, black plastic gyzmo that looks like a Whale's Tail and bolts to your AV plate just above the prop. With that and your engine in the closest hole, you can force the bow down and stop it.
