Until recently I've been using an Aptus 75 on my Sinar with the Linhof Rapid Slide adaptor.
It's in excellent condition and works perfectly.
It has the original box as well as the adaptor plate to mount on a Sinar P2 (other adaptor plates are available for Cambo, Linhof, etc).
This is one of the Rapid Slide adaptors that does not have swapable digital back mounts and can only be used with V fit backs.
The original price new was £1200 ($1900) for the Rapid Slide adaptor and a further £275 ($440) for the Sinar mounting plate.
As I have no further need for it and need to fund other purchases I'm asking only £450 ($720) for it.
I'm happy to post anywhere in the world but as the asking price is so low postage and insurance will be an additional cost.
Sam.