70 in a sportster? This is one where I agree with the boat's dream-o-meter. No way that thing can go that fast. 300HP skis top out around 70. You may want to try another app. As for porposing, I setup VTS on my Challenger to keep the nose down. It has the drivetrain from a GTX. I had to drill out the boss on the pump shoe for it. Not sure if yours has that same boss. It was all custom (wiring, switches, gauge etc). You can also buy some trim tabs. I've heard people like those smart tabs. It'll shave your speed though a bit.