Having done a few of these repairs, I am of the opinion that one is probably better off replacing the entire frame channel rather than patching. Generally speaking, rust damage extends far beyond what you can see, and the floor/channel seam is usually blistering apart along its length.
If one has local access to a willing HVAC shop, it’s no big deal or expense to ‘break up’ the individual panels.
Helps to have the dimensions, though, all of which are given in inch measure or degrees.
Bear in mind that I’m taking the measure of a set of panels I had made a number of years ago. While I’m sure the original measures are around somewhere, I don’t even know where to start looking. That said, on the inch dimensions, I’m trying to determine point to point either at the center of an apparent radius, or at a clear mark from where the sheet was clamped by the break. Each bend will consume a bit of material, so plan accordingly for the initial shear from the solid.
Material is .055″ common steel. Overall length is 66″, which allows for a bit of trimming of the compound end angles.
105.5-106 degrees. I think the half degree is simply margin of error. I was told at the shop that their tolerance is usually plus or minus 6 degrees, and I think they took the time to hit my target as I was not in a hurry and asked nicely.
This angle need to be the same as the previous. Again, measured out to 105.5-106.