An 1860 will be fine with a115/80 unless the boat is a pig weight wise, it won't scream, but it should plane out just fine. The funny thing a lot of people think the 2060 vs an 1860 will plan slower than the 1860 with the same engine, but you'd be surprised. The 2060 will draft less and actually plane out just as easy if not easier since it displaces so much water, the top speed will be a little lower. If you can afford it a 2060 with a 150/105 would be nice, you'd be amazed how nice the extra room is, and it's not in my opinion/experience any harder to launch or handle a 2060 over an 1860.
This is my personal experience I have a stout 1554 open hull tiller boat, it's heavy for a 1554 being a .125" hull, it shows it's scar having been used with a mud motor, a prop outboar, and now a jet outboard. I'm running an old evinrude two stroke 70 with jet so a hot 60/40 so to speek. It's perfect for that boat for all the more you can pack in it. I'm from Missouri originally easter weekend and snagging paddlefish on it is like religion to me. Couple years ago when I got married for my bachelor party we went snagging on easter weekend for it. Normally when I go back to snag that weekend it has been just me and buddy of mine maybe wife if she wanted to. My boat handles three pretty well, but that bachelor party weekend I for five guys, and couple big 40-60lb fish each I knew my boat wasn't gonna cut it. So I was going to borrow a buddies boat that I duck hunt with. His boat is a custom built uncle j flat bottom 2060, it's a tank 3/16" (.190") thick hull. He runs it with an old 1979 johnson 70hp prop with a tiller. Well of course about the time I was going to borrow he broke the plastic end of the tiller handle that the throttle twist grip goes on, the part wasn't going to make it in time for the snagging weekend. We could have pulled my tiller apart and swapped parts, but we had always been curious how my jet would push his barge since we were always impressed by how the little 70hp 3 cyl omc did with a prop on his boat.
So we swapped engines around he was running a jack plate that allowed us to raise up enough for the jet. Now my outboard jet was not ideal, but it did push that 2060 barge surprisingly well. With just two of us in the boat 12v troller up front with it's own battery, 12 gal of gas, starter battery, me 160lbs, buddy 190lbs, some fishing gear that boat did 27mph with my outboard jet, and planed out surprisingly well. Now when we went snagging the first day three of us went out, with cooler of drinks/food added, little more fishing gear, it still planed out surprisingly well, and did 24mph. Now once we got to snagging and we had a limit of paddlefish (two fish each so six total) which varied from 30-60lbs with that added weight planing out fully wasn't happening, but it still did 17mph, and because of how much water that hull displaces it was kind of planed out didn't really draft much water at all like 6" or so. I've launched that boat with my buddy while duck hunting when it's been just two of us plenty of times so that equates to one guy launching it really as the other just backs the truck in, and it's no more of chore to launch that boat or push it off a log than it is with an 1860. I have some experience with launching and getting an 1860 unstuck from mud/over logs. When I lived in Missouri while in college a friend of mine whose dad had an 1860 tracker grizzly with a 60hp yamaha prop which we duck hunted a a fair amount out of. Now that I've had a lot of experience with my buddies 2060 I'd go 2060 over 1860 the 2060 handles a load better with similar power in reality that newer 60hp yam was just as powerful as that none prop rated old 70hp my buddy runs. Granted these are props, but both flat bottom hulls that I've run with similar loads of 2-4 guys with decoys, and hard side duck blind and the 2060 wasn't much slower on top, but drafted less water, and planes out better, and is a lot thicker hull than that grizzly.
I'd imagine after having run my little 60/40 three cyl evinrude two stroke on my buddies 2060 I'd bet a 115/80 wouldn't be bad on it, and 150/105 would be awesome. If your planning on regular taking out four people with some gear, and cooler loaded down, and want a big trolling motor on it so you end up with 3-4 batteries, if you can afford it I'd go with a custom built 2060 and a 150/105hp. A 115/80 would work just fine, but a150/105 wouldn't give you some throttle to spare as already mentioned, a 250/180? or whatever it would work to at the pump would be if you just have the need for speed. This is just my two cents worth going off my experience sorry for the long post hopefully it helps in your decision. FYI if your willing to drive custom builders in Louisiana like uncle j, sportsman fab, along with a few others will build you a heck of hull that wouldn't cost anymore than the same size mass built hulls. But it will be a lot stouter. My buddies 2060 was really reasonable, but we wired it, rigged, and painted it ourselves.
