I think you will be fine using standard holders. 5x7 size fllm holders have been pretty-much standardized since the second decade of the 20th century. As long as you have a ground-glass back intended for film holders. The truth is, most cameras that were kept in use over the years were updated to take common standardized film holders. It "is" remotely possible you might get a back intended for glass plate holders, but I really doubt it. I have quite a few 5x7 size cameras from the first decade of the 20th century, and they all take standard holders.