It's not a jock

Moin@All,
as I pointed out beforehand, but in rather suboptimal forum, namely the welcome one, so I'm going to make a better job here.
I'm looking for good advice fixing the old diaphragm of my Celestion ditton 66, but combining new MD500 dia with old MF500 magnet/diffusor. But I don't have secure data whether if there a difference according the old and new midrange speakers, or not. So anybody may confirm this, or not, if you please! The main thing is centering the new dia after dissolving the old dia out of it's chassis. The cardboard spacers are destroyed obligatory in order to remove all adhesives from factory application. Now you expieriencing many parts, with no fittingsby their own, whether in the Steel chassis, or with the brown chassis made of bakelit, I presume. Shortly: the dia is surrounding the diffusor like a satelite it's star. How can I manage this? Any idea is welcome!
Furthermore I'm looking forward buying a complete MD500, in working condition, with a fair price. I'm not about dumping any offer, but I'm far from paying moon-claims.
Ah, important to announce: I'm out of any professional measure devices! There is a multimeter measuring impedance, and finish.
Tschüüß, Peter