I'll just say that the missing spring could be your problem. You will soon know. When I was working on my 59 it had a foot start. I needed to fiddle with the carb and timing. So I operated the lever so that it would start the truck. I had my front clip off so it was easy to get to with a wooden stick levered against the firewall. I had the key on, in neutral and Ebrake on.
You can operate the lever by hand if you want, at your own risk. I believe you realize that just pushing the button will not slide the pinion, it will run the starter and not prove anything. The lever slides the pinion into the ring gear and then the same lever depresses the button. I pretty much said all that in the previous post. I recommended testing with battery disconnected to observe operation because I don't know how savvy or careful you are. That is not an actual full test. It will test the spring return and it will show any slop in the linkage. Be careful. I think you will have success. Let us know.
P.S. You say spring was missing, you say will try tomorrow with spring in place....so you found the spring? Where was spring when you took the picture showing it was missing?
