'68 gmc cummins project

[Str8-6-68]

Hey guys I'm new to the chevy/gmc forum but my project truck is a 68 gmc long box 2wd. hopefully this project keeps me busy for a while as i want to shorten the frame for short box and swap front cross member for a 98.5 24valve 5.9 cummins turbo diesel with lots of work done, I was also thinking of closing in the open channel frame for a box frame. my goal for the motor is in the 800hp range give or take on a single turbo so I would love some feedback on some of the best rear end gears and axel shafts to use, as the engine to be built will put out estimated 1200ft.lbs. I was thinking of doing a 2wd chevy 2500 front and rear 8 lug conversion including rear diff but i would rather keep as much off the '68 as i can except drum to disc and beefier suspension. any and all information on the suspension and rear diff to handle the added weight and high torque the engine will put out. I would rather find gears and axel shafts for the '68gmc to handle the power than swapping for 2wd dmax setup. Thank you in advance for all info.
-Allen