I would like to be able to have more control over my vehicle (because not being able to play with stuff is just wrong) so my question is: would it be possible to convert my 99 gt distributor to the older adjustable type or would i be better off using some sort of computer to play with my timing? my only other option would be to change my timing when i do my timing belt. but this has lots of limitations of course. my main goal is raising my mpgs.

Piggy back or stand-alone engine management are what you will need.

since you are ODB II you cant advance the tuning. I dont know of any piggy pack that can advance timing, only retard it. you can get a stand alone like the AEM EMS 4. but you have to wire it in

If your car is running perfectly, I recommend looking into a MegaSquirt-II. There's nothing for our cars that is plug and play in the EMS area, so all installations will be custom, and have to be made by yourself. MS-II offers what most other ECUs offer, without the hefty price tag. However, it requires more user-involvement.

As for changing distributors with the stock ECU, thats a no go. The fuel system also runs off a signal from the distributor.