I'm having trouble replacing the throttle return spring. I can't figure out how the loop end of the spring, the end farthest away from the Carb, is secured. If I had a picture of that I could figure it out, I think. It is a 1931 type spring
It will be a heck of a lot easier to simply remove the assembly. I don't think you can even put a new spring on unless the assembly is removed. While you're at it, with the old spring removed, you can pull the upper shaft out a ways to clean and oil it. Use a drill bit to manually clean out the two oiling bores on top of the main bracket. They usually get clogged with gunk and make it difficult for the accelerator linkage to swing freely back and forth. Then put oil down into those bores and work the shaft back and forth until it flops easily before the new spring is added. You will need to tie or hold the accelerator arm against the assembly when slipping it up between the engine block and firewall. Then draw it against the engine block with the two large bolts. Don't put a lock washer beneath the bolt head on the driver's side. The accelerator linkage that you push against with your foot can be hindered if that bolt head sticks back too far. That will prohibit reaching full acceleration at the carb. Or you could just bend that portion of the linkage to clear the bolt head.
Marshall