I have built spacers for a lot of bikes..
I start with blocked up bike. Then put wheel without spacers, on the axle in the frame. Use a thin straightege to line up the sprockets, using the back sprocket.. When they are lined up , measure and build spacers.. Simple proces, 'cept maybe getting spacers made.
Tip shortening a short spacer , usually not as easy as it looks, sometimes easier to make new one.
If your axle has a nut/hex on the end, its the later longer axle.