no you do not replace the doors you can buy a hinge kit for around $1,000.00 and I would bet that it would cost you at least another $1,000.00 to get it installed properly if not more. and in the end all you will do is turn a cool f-body into a ricer. THAT IS NOT COOL!!!
on a side note those doors are rather heavy and if the shock that holds the door up was to give out the door could easily break your leg or worse. and again that is not cool.
The money would be much better spent other places on the car. like performance upgrades maybe a nice Stereo or many other things.
PLEASE do not desecrate a truly cool car by turning it into a ricer