I have tried a few Rolleiflex strap options in recent years, with differing degrees of success. I had the original factory clips riveted into a new strap by a local leather shop for the same price as a belt, it works well on my 'E' but sadly would not fit on my 'C'. I learnt of the different strap connector sizes and styles the hard way. I found that barton1972 straps do a dedicated Rolleiflex leather twin thin prong kind of thing as an option which totally rocks but my local stockist didn't have one. He did have another strap by that same company which is a kind of blue suede and super, super thin at the ends. Maybe 2mm tapering up to 5mm and then into a full width strap. With extreme care I was able to thread this perfectly onto the camera and the weight hangs across the full thickness of the strap, plus it looks pretty cool.
Others have reported a simple but sure success route using the Optech straps with the thin nylon string hoops. I had one of those on an F5 years back and from what i recall, I'm sure that would work also. I know that none of the above answers your question exactly but was just hoping to help share ideas. A Rolleiflex is so much better when you have the strap situation sorted out properly! Don't be tempted to jury rig it by forcing metal keyring hoops through the holes and attaching regular camera straps, it basically works but looks terrible and is bad for the camera.
