I can only answer 1 of your questions, and guess at the other.
I would guess that the seats will fit the rails. As far as how well they'll orient in the cabin, I don't know.
One of my seat posts rusted out as well. You might check - mine actually rusted from the INSIDE out on the drivers side front right. To "TEMPORARILY" fix the problem, I cleaned up all of the surrounding rust. and then took a stainless carriage bolt and 2 LARGE heavy washers and put them on the bottom side of the car to spread the stress out a bit. I then sprayed rust proofing goop all over it. Someday, I may have it just welded up as it should be, but this solution was cheap and easy....