what car? i guess should be wira right?
at gearbox for wira 1.5 is simple.
not so with 1.6 as it comes with electronic overdrive (the 4th gear ratio). i think even the torque converter housing also cant fit with 4G15 block.
most important, u need to find one unit gboz, complete with its ECU and wiring. but easier still, convert to 1.6 auto. or change car to 1.6 model. even the 1.8 EXI is cheap nowadays...of coz the SOHC one. but u get ABS and additional 200cc advantage to 1.6.
if 1.6 is costly, try finding lancer half cut with 4G91 1.5 DOHC 16v auto. u get to change complete dashboard too, but normally comes with digital aircond. the 4G91 is using 3 speed + overdrive also.
the reason why proton dont want to use overdrive auto for wira 1.5 is simply becoz of cost. u need and ECU to make the overdrive work,such installation will hiked the car's price up easily 5-6 thou.
as to what u r thinking, its not worth it. sell proton, and get some other makes...:D