15x10 fitment on non-tubbed Duster

No offense meant, but good luck with that "day two" thing. Most true day two wheels, mags anyway, came as one piece, no choice of offset. I think you will run into the same problem with one piece wheels now.
I have some new 15x10 vn105 one piece TTD that have 3 3/4 bs, so same problem as your keystones.
I also have a pair of 50 year old ansen five spokes, and a set of four 200s daisies, all 15x8 1/2, all 3 1/2 bs. They are all difficult to get on a car without a full open wheel well.
I think if you really want a day two look, you are gonna need a two piece varient of an original one piece wheel. To me, that means a tt2, or a 200s. TT2, are very common (maybe because they can be made to fit) and daisies (200s) are crazy expensive, maybe why they are UNcommon.
Again, no offense, but maybe if you scaled down to a 15x8 or 8 1/2, you would end up happier, with less work. You can still get a bunch of tire on an 8 1/2 rim.