I discovered some of the problems.
I was looking at pics from Moss and AHSpares. On the new ones the back rest is straight looking from the center top to bottom. Mine had a slight curve at the last inch or so in an 8-inch area of the middle. Probably from years of use and abuse. A little creative tin knocking flattened it out which also pulled it down and back. It now rests very close to the tabs on the bottom where it’s supposed to.
In addition, I noted that the ½” lip on the bottom of the seat back that sits on the tabs is a little weakened by wear, rust, and someone creative tin knocking. I will add some extra support to that lip probably with some sheet metal 2” wide (tabs are1” wide), bent at a nearly right angle on the inside, epoxied in. Does anyone foresee a problem with that plan?
I also plan to glue on thin rubber bumpers on the frame tabs and the bottom lip of the seat back. Sound like a good plan?
On the seat pan that wouldn’t fit down into the bottom frame,I noticed that in the front where the pan is at a perfect right angle looking top to bottom in the AHSpare pic, mine bulged out some on both sides. Again, alittle more tin knocking and it fits into the frame now.