2nd post on this.
I've been running 18-40 hp 2-stroke prop. units on the Tanana, Yukon, and Cosna Rivers since '75, and Yamaha 4 stroke 40/30 jet on Tanana and Cosna since 2012. Frequently over-loaded. Occaisionally to the point not getting it on step (down-river, never up-river) Same boat all that time - an 18 foot riveted flat bottom. Not a Lowe from the looks of your pic. Those motors have always gotten me there, assuming mechanicals stay on line...
. Eventually. Bush time works for me. ( Pushing to meet a time-line is a mistake!!! It can kill you.)
A 50 hp powerhead with either prop or jet on your boat as stated should do you fine, tho not necessarily speedily. As mentioned, jet units up here are hard to come by.
I'd buy what I need Outside, and bring it up with your boat (assuming you already own/buy one there.)
I have also run 18' Grumman canoe with side-mount 4 hp Merc on Cosna and Tanana bertween my cabin and Manley Hot Springs. That 35 miles upriver from the mouth of the Cosna to Manley, on the Tanana, takes awhile thusly, even with just me, my survival gear and a Lab ( or weight) up front in the canoe for ballast.
The 20' square stern with 10 hp 2-stroke did it better, but got stolen.
One time, early October (checking on squatters in the cabin) I broke ice with the 18' Grumman, going down the Cosna from my cabin. Canoe still bears the dents. The Tanana, once reached, running slush, was no problem, even going upstream back to Manley. About 8 hours IIRC. I should probably sell that 4hp, 2 blade, '62 Merc....
Naw... I might need it yet. Might get a spare prop for it, tho, if I can find one.
It beat waiting another 6 weeks or more for freeze-up, tho.... then I'd have had to walk the 50 miles. Probably would have kilt myself on/in the river.... Happened to a neighbor about that time of year one year.
Damn - Did I had fun when I was younger, or what???!
Seemed "normal" at the time. Still does, but I have gotten lazier.