A 70 HP will blow not only your mind away, include yourself out of the Rib. Have you tested the combo package previously at wot ? The issue with a 70 HP motor it's darn s too heavy, will need a heavy champ to sit as a bow mask up front to balance and distribute the deck load evenly across the entire hull. If not the boat will achieve a bow up attitude.
Personally wouldn't dare install a 70 HP motor on a 3.65 Mtr Rib rated for a 30 HP motor, max would be a 40 HP one. At wot that boat should have a nervous behavior specially if tiller driven which don't know if it's the case ?