alright. possibility of owning a 90 bii 2.9l 5spd 3.50:1 gearingl... i have an 87 bii intake (the bigger kind) to fit this and the computer. what kinda mileage will i be able to expect if i put on dual straights and 28" tires also?

 

17 city 21-22 highway

Any mods you do will likely increase performance, it will not likely increase MPG, from experience.

 

3.50 gearing? I'm not aware of such R&P set for a D28/D35 TTB or 7.5/8.8 rear. 3.45 or 3.55, maybe:

Ford Ranger Axles - The Ranger Station

Computer change-out isn't a necessity with the throttle-body swap - unless you plan on swapping over the EGR and other pre-'88 stuff. All you need to do is swap the throttle body, not the entire intake or upper intake. For best results, you can port match upper and lower intake (either the '90 or the '87), clean up the throttle body bore edge(s) for smoother airflow, and you should be good. I would vote for keeping the '90 intake and just swapping out the throttle bodies and leaving the '90 computer in. Hope this helps