Am I correct that the tank was sitting against the wall with the water supply sticking out of it?
I don't know if this is viable or not, but let me mention this: The 12" rough-in Drake actually has 1-1/8" behind it, so you can get it in on an 11" rough-in, and, usually, on 10 7/8. This despite the fact that some of the spec sheets say 3/4" behind, and some say 1-1/8".
The spec sheet for the 10" rough-in Drake says 3/4" behind. If, in fact, it has the full 1-1/8" that the regular Drake does, then you could get it in on a 9" rough-in. I just don't know the answer, though. Maybe someone who knows can champion or bludgeon my idea.
You can get the Drake in with the water supply only a smidge to the left of center, but that looks maybe too tight; I'm thinking that you may need a 90 out of the wall. Certainly if the Drake idea is viable, we can measure and figure out the rest.
The Drake is 19.5" wide, so you've got 2-1/4" on the one side. It'll fit; maybe not the most comfortable. I don't know about where you are but code is usually 15" from finished wall to center; I'm assuming this isn't somewhere where it needs to be inspected?
EDIT: I guess I should point out that, as Jim notes below, the right (and, depending upon where you are probably the legal) thing to do is move the drain. My thought was "Poor guy, pulls up toilet and discovers horror. Maybe this could give him a quick and admittedly-dirty solution." What Jim says is correct, of course. Sorry you couldn't just reattach your tank with a decent set of tank-to-bowl hardware.