jeep grand cherokee 5.2 as donator for my dart gt -65, what gearbox should i use?

You can't easily use a 4-wheel drive transmission in a 2-wheel drive vehicle. You would have to change out the overdrive assembly for a 2-wheel drive overdrive. Then there would be a fair amount of chassis modification to get the overdrive to fit. Or, you could convert the Dart to 4-wheel drive, but that would require a substantial amount of chassis modification.

What engine was in your Dart previously? The 5.2 Magnum will adapt to a V8 Dart transmission with minimal hassle (you will need a torque converter register bushing to use a 67-prior converter with a 68-later crankshaft, or replace the front pump and input shaft in the transmission with 68-later parts). Also, the shifter in your Dart is only compatible with 1964-1965 transmissions. A later transmission generally requires a change to a later shifter or an expensive adapter cable.

The Jeep rear axle is most likely an 8 1/4" axle, which is stronger but too wide for the Dart.