HI,
There are six versions of the early Camera Holders before the VT holder was released in 1956.
It is all to with the cut-out on the side and the internal groove that is below that cut out section. Also in the chrome arm as supplied with later holders, there is a groove cut into it so that models with the later strap lugs can be placed vertically. It is to do with the half moon strap eyelet being 2mm wider than the dog eared version.
So before you buy any bottom loading holder check with the seller what model camera he is selling or owns.
Oddly, Canon never made a Camera Holder to fit the Model 7s or 7sz bodies...why beats me. I can find no reference in any Canon literature in regards to a holder for them. The Camera Holder for the 7 does not fit the later model because of the position of the tripod hole. Cheers Peter