Found a good writeup by bsilva132 on sill replacement
https://forum.ih8mud.com/40-55-series-tech/115925-wheel-well-rear-sill-channel-repair.html
He made a rear sill out of 2.5 x 2.5 x .25 box beam and then tapped the bolt holes for tire carrier, tub mount, and latch point. I liked that idea, but did not like the 2.5" diminsion. The original was 2.25, so my fear was that you are raising the back of the tub (as it attaches to the frame) by .25. I don't think he used a sheetmetal cover as original to tie into the floor, so he may have been only off by 1/8, but alas, I used a 2 x 2 x .25. This allowed me to then to have a .25 area under my channel to weld some spacermetal .25 with nuts for the frame attachment. The sides (curved sections) are also .25 metal that I bent to fit.
Now, this is where I have to gloat. A year ago I got $100 of metal and a bunch of scrap metal that had been setting in my shed for years and spent a weekend welding up a rotissarie (car spinner). It has been great, but when I started working on this sill, it was awesome. As everyone knows, don't #uck with Newton. Gravity always wins. Well, the sill comes out from under the tub, and I was having all sorts of problems fitting the new one without a spare set of hands. Then I spun the tub over, and all was solved. It was great. At any rate, as I promised when I made the spinner, I will rent it out to a TAC member to use, with the rent going to TAC. I should be done with it this month, so if anyone needs it, let me know.
After I welded the new sill up, I tapped the bolt holes, cleaned it up and POR15 was applied.
The new sill skin was bent on a brake at metal by the foot, and cut to fit. I had to cut off about 2.5 inches of the old material to get past all the rust. I POR15 this also before I installed the sill behind this skin, so it won't be a haven for water and rust.
The last pic is upside down, well actually the picture is right side up, the car is upside down.... I love that car spinner!