New Member with a big project in the works

[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. 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. Thank you in advance for all info.
-Allen