I've just bought a wonderful Horseman 985 mf field camera with the 69 back. It is a really great thing to use. I have an old mamiya rb67 back hanging around which I want to use on the horseman. The plastic plates on the interface part of both the mamiya and horseman backs look identical. Without measuring I can't see any differences, yet I cant get the retaining sliders on the mini 'graflock' back to fit with the rb67 back. Does anyone have any experience with this issue? Is there a modification that can be made to the rb back to make it fit? I've googled but can't find a definitive answer. I can wedge the back in place, and it works ok, but there are a few light leaks so it's not really a solution. Thanks in advance.