Replacing weld nuts for front bumper bkt

While mocking up the front end pcs. on my 66, I found something that's going to not be fun to fix. The weld nuts that hold the front bumper support brackets on the Pass side have broken loose of the frame. (I now now why the brackets were in the trunk when I bought the car) I managed to get the bolts out by prying outwards while turning the bolt with an impact. Unfortunately, the nuts pulled through the frame (the rear almost completely and the front about 1/2 way). There is no rust on the frame that I can see, the damage was purely from the impact and prying. The metal is solid. Nobody makes a repair for this and the backside of the frame rail is not accessible when installed on the car. From what I can see, the nuts were installed on the frame rail prior to it being installed on the car. I don't see this as something that neccesitates frame rail replacement. Has anybody had to repair this? Here is my current plan:

1. Open up hole diameter large enough that a new nut will fit cleanly into it.
2. Take a small pc. of sheet metal, and drill a clearance hole for the bolt.
3. Weld nut to backside of sheetmetal.
4. Weld sheetmetal to existing frame rail, with the nut inside of the original frame rail hole.
5. Smooth welds, prime and repaint frame.

I figure this will allow me to mount the bumper and reinforce the original frame in the area where the weld nuts are. The repair will not be visible once the bumper brackets are re-installed....Any thoughts from anybody?