The best way, by far, to get all you want, is to use the cab and front sheet metal on a short bed, 1/2T chassis....or maybe some other UTE.
Any other way will take lots of skill, time, money and parts.
3/4 ton have 8 lugs and don't come in short wheel base.
Your list is very good but very restrictive to much of the existing truck.
1. You want the original truck to be represented.
2. You want it low and short to fit a garage.
3. 6 lugs
4. Driver quality comfort and reliability
5. Flatbed
I commend your goal. A family tribute. Maybe you can use the headache rack and some of the bed lumber on the new flatbed.
