I've run a few jets on different hulls, mostly in the last 4 years. What I know for certain is that a 4 stroke jet uses less than half of the fuel as a 40/30 2 stroke-of any brand. You may find that you may be a good candidate for a 40/30 4 stroke jet. You already know one downside of a jet (excess fuel usage), but also the noise issue is there. The 40/30 Yamaha's I've run are no louder than a 2 stroke with a prop. Usually slightly quieter even at full throttle. They work awesome for skinny rocky bottom areas. The hull is a BIG part of the equation too, and there are hulls specifically designed for one of the most well-known rivers in the US (White River in Arkansas), that are designed to run a jet with a small tunnel. They typically have a draft of a few inches when on plane and yes I've run them in literally inches of water dragging the gravel (rentals). I do not know your rivers but the White is wide in most areas and about a foot deep in a lot of areas. These boats (supreme, Shawnee, topwater, etc) are designed for drifting and running these areas, and they do it extremely well. They're on plane almost instantly despite the length, the banana shaped bottom with no strakes and ribs will run real shallow and if you do get stuck, just walk to the other end of the boat to rock it off. They do not handle very well in a turn though, and they do not take side-wake all that great. I'm not sure there's another boat that would do that job any better on the upper White river, but again I'm not sure how the areas you fish are similar or different since I've not been there. Might be worth looking into, though.
I've run my propped outboard on the white and you do have to be mindful of where you are at in relation to the bottom. It's misleading and kinda stressful because the water's crystal clear and you're watching the gravel rush by you at 25mph (upstream) thinking that anytime now I'm gonna rip the skeg off. Really I'm using the wrong tool for the job, which is why a couple times a year I'll rent one of the jet outboard boats for a few hours.
The evinrude 48/35 cannot be compared to a newer 40/30...the newer ones are FAR superior in every way.