First, let me say thanks for maintaining and contributing to this forum. I've spent many hours browsing and searching the posts here, and have learned a ton. I think I have a plan, but I wanted to be sure I'm on the right track.

I've created an album in the gallery section under my username: http://www.hardwoodflooringtalk.com/gallery/thumbnails.php?album=47

I'm not a professional at this, I'm a homeowner with fair-at-best carpentry skills. Home was built in 1856 as a Methodist church, then gutted and remodeled in the late 80's. I've been in the house for 6 years, so I wasn't part of that effort. There is a crawlspace, about 18" high from the ground to the bottom of the only beams I can see. The only access to that space is a small cutout in the foyer closet. I have seen plastic attached underneath the plank subfloor, but I have no idea of the condition of that barrier. The crawlspace is vented through the stone walls in two places on each side of the house.

-Plan is to install engineered in the living room and dining room, about 485 sq/ft, mainly because of the crawlspace. I wasn't confident using solid wood so close to grade.
-My intention was to staple the flooring, but I found a product that we really like that's uni-clic (Award flooring Country Relic Cottage Brick), which would force me to float or glue. Jury is still out on that. I've also been looking at Anderson's Virginia Vintage line, and a couple of others. Trying to stay in the $5-6 range as much as possible.
-Current underlayment is 1/2" OSB, over what appears to be plank flooring, also 1/2". There is also wood underneath the plank, but I can't really tell what it is.
-Moisture readings with my Lowe's meter on the OSB in both rooms all fall between 9% and 10.5%
-Joists? My guess is that this place has logs for joists. The floor does feel solid, other than a few spots where the OSB could use some screws.

The problem: A hump running front to back that's nearly an inch high over 8' or so. Common sense, and all the reading I've done here, would suggest that it makes more sense to bring that hump down, rather than bringing the rest of the floor up to meet it. To do that, I'd have to cut out the OSB (wall framing is resting on it), then sand or plane the plank flooring underneath (only 1/2" thick planks, over who-knows-what).

So my plan at this point is to lay down 3/4" ply, maybe Advantech, starting at the walls, up to the point where the height would be equalized, then shim in the rest with thinner wood or shingles. I did this already in the dining room, where the problem wasn't nearly as pronounced, using 1/2" and 1/4" ply, along with shingles. My only issue with this approach is that I'll be left with two transitions that will be about 1" higher than existing tile in the foyer, and linoleum in the kitchen. I also have a pellet stove sitting on a 2" marble slab that I'll have to deal with.

Is this my best option? If so, should I use T&G plywood? I had one installer suggest using SLC. Looking at the Ardex site, my guess is that I'd need 15 or more bags, not to mention the goat rodeo of trying to mix and pour 5-gal buckets fast enough to level before the stuff sets, and the added cost.

I appreciate any suggestions, tips, or warnings