So I borrowed said friend's analog joystick and measured the resistance between its extreme deflections, took apart an Atari joystick and then soldered resistors into its circuits to simulate full deflection... then got some multi-conductor wire and laboriously soldered it to the tiny pins on a DIP connector, which was what Apple computers used for joysticks. I don't remember if I had to figure out the pinout or found it in the Apple manual.

This all worked, but the connector was too fussy and fragile to be practical. Funny how much stuff you could learn in a reasonable time with no Internet, no car, no access to an electronics clearinghouse like Mouser...

I must have gotten all of it from Radio Shack on my bike. I wrote the whole procedure up and submitted it to Compute! magazine, but I don't remember what their response was. They probably concluded that not enough people hated analog joysticks enough to go through all that trouble.

Understanding it was switches, with a wire, I worked out & documented the pinout of the DB-9 connector (afterwards, my father showed me it was documented in the C64 manual).

At some point, I took the remote from an cheap broken RC car, and soldered the switches from it to the cable of a broken joystick. I found a switch in my father's parts bin for the fire button. It worked, but it wore out pretty quick - the RC car controllers switches weren't built for gaming use!

I wish I had photos - its long gone.