i have a 91 gt aod and i'm lookin to upgrade my distributor from stock. what is the best distributor for an e303 cam? and what's the best ignition to go with that distributor

I did a little research for you and for the cost and ease of installation the MSD-6421A-K. This is all prettu much plug and play stuff for the car, here is a link to the website if you want to check it out.........

i was lookin at that set up but the distributor says for use with factory roller cam. is that going to work with a ford racing e303 cam?

Yes! It states that because the gear on the distributor. The roller cam takes a steel gear and flat tappet are cast. If you use the steel gear on a flat tappet cam it will eat the gear drive on the cam and the same goes for a cast gear on the roller cam.