the outter dimensions of plate holders are pretty much the same as film holders.
i use film holders in a plate camera all the time without problems ...
as long as you are stopped down a little bit you probably won't have trouble with
the whole thickness-thing. don't forget that film sheaths / septums were traditionally
installed into plate holders when sheet film started to appear on the market. the septums
do not bring the film to the same focus plane as a glass plate. stopping down a little bit
will probably correct for this problem.
after reading the link, maybe i better say,
that the plate and film holders *I* use in my
cameras ( manhatten wizard and delmar )
can use modern film holders without a problem
and the modern cameras i have ( graflex/graphic, toyo and szabad )
use wooden plate holders without any problem.
i never saw that thread keith referenced, and i didn't realize
that they weren't interchangeable ... sorry about that !
i love this place, where else would one learn such random and obscure information !
I've used a modern 4x5 filmholder in a little 4x5 pony-type plate camera. It fit perfectly. At some time in the past, a previous owner flipped the ground glass around so the matte side faces out. This would move the focus about the thickness of a glass plate. I had no trouble making a sharp image on film at about f/11 or 16. I did the same with a 5x7 Seneca Black Beauty I own and have been able to make good, sharp images on film.