Niiiice hardtop! What engine? Beware the early 5 speeds, most were for 4, 6, and small 8 cylinder engines. They were weak. There are very strong 5 speeds that cost plenty. It's better to get one that fits directly in place of your T-10, and the shifter placement will not be a problem inside. This guy did it:TKX pic Also you must match the 5th gear overdrive with your rear gears. Even though these trannies are very strong, you can break them if you try hard enough. My buddy has a '55 Chevy, mountain motor BBC, and he managed to break the TKO 5 speed.
What is your complaint? Too much rpm at highway speed? What first gear in the T-10? A T-10 is the old version, are you sure it is not a Super T-10? Anyway, before overdrive, GM made 4 speeds with ultra low first gears. Paired with granny gears out back, it worked well. I have a '79 ST-10 with a 3:42 first gear. I had 3:08 rear gears in my '77 TA. 3.42 x 3.08 = 10.5 overall ratio. You can climb trees with that. Then the 3:08 rear gave me 60mph at 2000rpm.
