Allen Friday had the holder that is similar to yours and we used it for wet plate. He showed me how he had simply cut it down on the sides in a table saw. I don't recall if he did anything else to make it work. I don't know if it had a slot or rib that worked with his camera, an 8x10 Tachihara, but with a good dense darkcloth and the collodion there was no fogging of the plates even if there were any gaps. I know the T dimensions for his holder were compatible because the plates we made were sharp. I sent him a PM about his holder but if you contact him directly he could provide some specifcs. Yours might not be exactly the same but from what I recall it sure seems the same.