Unfortunately, the back sizes and pin spacing are all over the place, depending on the camera brand (ask me how I know). The only positive info I know is, backs that fit a Burke and James 8x10 will fit on a Kodak Master 8x10. But, I have a Century 8x10 sitting on my shelf (bad bellows, or maybe no bellows at this point) and (I think) some 4x5 reducing backs of unknown provenance-- I'll see if I have one that fits. I guess you're used to lugging an 8x10 around, but part of the point of 4x5 is how much more compact it is. You might want to pick up a cheap 4x5 anyway even if you get the reducer back.