The biggest problem with any of these lifts is that the door has to be PERFECTLY placed to install it, we are talking it's tilt, its height, it's in and out movement at top and bottom, all of these have to be near flawless to put the bolts in. If the stand changes or the body is moved at all from when the door was removed, if this relationship changes in any way you will need to make VERY precise changes to be able to put the door back on the car.
I have hung more doors than there are characters in the posts of this thread and that is the one thing that pops into my head when I think of these stands, I have tried them. I have tried a number of different ones because I used to work by myself, a one man bodyshop. I then worked with a guy who was an Einstein like character who would make and design tools everyday. He made a few different versions of these tools, they all failed.
If you were working on ONE car like that beautiful Pantera (STUNNING work you are doing there) with a body on a rack that doesn't change and a perfectly flat floor and such yeah as long as the door rack adjustments don't get changed you can put the door on the rack and wham, roll it up to the car and bolt it on.
But if that adjustment gets changed, the entire plan is down the tubes. To roll the door on the rack up to the car and then adjust the thing and all the angles needed to bring that door up to the precise spot to bolt it on is going to a HUGE undertaking with you sure to end up chipping the paint.
Can it be done, sure, but getting help in some way is going to be so much better.
I am not arguing that it can't be done. All I am wanting to express is that the time spent making up something like this for most of us would be better spent on other things that would move the project forward. The bolting and the unbolting of the doors in place are a MICROSCOPIC amount of time in the grand scheme of things. When you think about the hundreds or thousands of hours spent on one of these projects the three and a half minutes it takes to bolt the door on the car is pretty small.