The seatback doesn't sit lower than the bottom cushion. Remember you have to tuck the bottom under the seatback when re-installing the bottom?
I think it'* fairly doable, but you will need to make sure you have a good latch setup. You'd also need to make a good backing plate for the seat as the foam isn't very sturdy -a good tug when you thought it was unlatched would rip the screws right out of the cushion.
For the latch, you could just cut a notch in the rear dash cover and bolt it to the top of the dash and do a cutout in the top of the seatback where'd you install the part of the latch that is on the seat. Would also be cool to convert the seat to a 60/40 split so you could just have one part open if you have 2 passengers.
This project is VERY doable and I bet it could be done in one piece form for under $100 dollars and if you were to make it a 60/40 split back it'd probably be another $50-100 to the upholstery shop and some pocket change for the aligning components (to keep the bottom of the seat backs even -possibly another hinge at the inner side of the seat) from a car in the salvage yard.