The '68 I did many years ago had the 6 cyl, A/T, P/S, A/C set up. It had a smooth acceleration with respectable freeway performance. Certainly no tire smoker, but a smooth operation. I drove mine to work daily on the expressways and had NO problem mingling with the other traffic. The fact that your car is a rare 'T' code would (in my opinion) make it as valuable as a V-8 easily, maybe even more so. The only mod I would consider maintaining is the V-8 suspension assuming it was done correctly, and if the front coil springs aren't too stiff for the lighter weight engine. Also, V-8 drum brakes would be more efficient. I think the drums & brake shoes are about 1/2" wider than the standard 6 cyl brakes. AND you have the Shelby wheels that look great (with the 5 lug drums). Go for it - you won't be disappointed.
Neil Hoppe