If you didn't discard the brake shoes measure there width ie 2 in, 1.75 and so on. Then measure the backing plate. With these two measurements you should be able to figue out which parts you need.
That looks like it in very good condition. My 40 is in pieces. You might do an internet search and find something. Good luck with your project, you've got a great start.
When I was building dune buggies.We bought a manual push/pull switch that was made to go into the rear brake line. I don't know if these are still available. They worked good on buggies.