I think you are planning something like I just made for my smoker. I didn't have a plasma cutter so I cut them with an acetylene torch. They are 3 piece with the hinge being the full width of CC door. I pulled the door down to fit the CC with a come along and then welded the hinges on and let it cool good. The door stayed in place when I released the come along.
To make a sketch - drawing of the hinge I cut a piece of cardboard that fit against the end of the door cutout on the CC and drew the radius of the tank and then moved the cardboard down how thick I wanted the hinge then drew the outside radius of the hinge. Then I just extended out the hinge to make it as long as I wanted it.
Bcf, I was thinking of doing something like that on my current build, if I started to cut out the door, just where the hinges would go. Weld on 2, maybe 3 hinges like yours. Finish cutting out the door, it would hold shape? My tank is about 53 inches between the welds for the end caps, so door could easily be 4 ft long.
Mofomatic, I cut my door out completely first, then welded on the strips around the edges of door. I cut it with grinder and cutting wheel and it warped just a little which I was able to nearly straighten out. When I pulled it down with a come along before welding on the hinges it pulled down to the CC and it stayed in place. I would be afraid if you cut only where the hinges went and welded on the hinges it might warp when you finished cutting out the door. I think I would cut the door leaving 4 or 5 inches on all four sides, weld on the hinges, let it cool good and finish cutting the door.
ABBOV your hing design will work great i made my hinges exactly like yours here is how mine turned out. Also this design allows you to install a hidden door stop in the hinge on the CC side notice how i have the back plate on the 2 vertical pieces i notched a V in this and adjusted the notch so the doors rest just past the upright center line off the smoker so there is no risk of the door falling back forward on the cook