I have a Kodak Brownie Reflex camera which has a nice sized viewfinder. It also has spots and dirt that makes for a cool image. I made an TTV adapter for the Kodak to use with my Olympus OMD-EM1. I constructed the adapter out of thick cardboard, like the back of a watercolor pad or something like that. I always save these pieces of cardboard for projects. The diagram for cutting out the shapes is shown below.
I glued the adapter together with hot glue. I also strengthened the adapter with duct tape. Below are some images of the finished adapter on the camera.