The Ebay auction has too little visual information to make an educated guess about the conversion and the effect on the mic's value: capsule, inside amp or power supply are not shown. Also: the connectors are not the original Tuchel type, but East German copies which are not compatible with Tuchels.
If the mics were indeed "factory" converted to U67, there should be a Neumann-issued document. If not, the collectible value suffers, and the mics' usefulness as a recording tool will be your guide for pricing.
Always think of the other end of any Frankenstein mic: how much explaining will you have to do, when it's YOUR time to sell?
Take all of this into consideration before you bid.