FWIW, I have a 6hp Tohatsu (they manufacture small hp, 15 hp and under, for Yamaha, Mercury, Nissan) on my Hyde LowPro! It will get you back upstream at 3500 CFS; as long as you are not in a hurry (with 2 persons and $h!t loads of gear)! An 8hp should be ideal. Onlineoutboards.com is in Dickson, TN, and has reasonable prices. YMMV
Jim