Hi John, looks like a good project, my old one is buried in this thread somewhere but here it is on CCMV http://ccmv.aecsouthall.co.uk/p411439082/h2e0b3959#h2e0b3959
A 35t Crusader 5th wheel will fit fine, only the release handle is different. I can provide a rough sketch of the mounting adaptor if you don't have one.
Has the rear crossmember been removed, I can't see the towing eye and winch rollers?