TheoULF
i was not able to see the faceobook photos, unfortunately ...
are the plate holders inside the camera, and like sheaths to put
the glass plates in, or do they look like modern film holders but for glass plates ?
if it is one of the ones that has the septums/sheaths inside the camera, it is a falling plate camera
like the box camera where you used double sided plate holders there were many makers.
western camera manufacturing company made lots of them ( there was usually a tag ).
sears also had them made for them and often times did not have a manufacturer-tag
this link:
http://web.archive.org/web/20041123084139/http://www.boxcameras.com/camcolhome.html
has a lot of box and falling plate cameras maybe you can find one that looks like yours ?
i don't have / use ones that are 3x4 but 4x5, i have a few falling plate versions ( cyclone 3 and 5 ) and one that takes film holders ( delmar )
lots of fun to use them !
good luck !
john