Bryan Darling

Hi, I have an original Rex w/o the variable shutter. It has a 6x viewfinder which is quite a pain to focus. I'm curious if anyone has knowledge in regards to changing out the viewfinders. I noticed that the finder seems more permanent than those on the non-reflex models. The problem would be finding a 10x or 13x viewfinder and then knowing how they are attached in addition to anything special in regards to the position of the finder, for proper focusing, etc. Thanks, B-