It is only the TTL metered finders that are not interchangeable; i.e the 67II AE meter finder will only work on the 67II and the 67II can't use the earlier TTL finder. The 67II can use any of the earlier unmetered finders and the unmetered finders sold with the 67II will work with the earlier models. AFAIK there weren't any changes in specification for the unmetered finders, so a pristine old one should be just as good as a brand new one. Having said that, almost all of the prism finders that I have seen look to have been dropped at least once. Any of the WLFs should be just fine.