The one hub I haven't got in my backup arsenal is the FH-7700. One of these days I'll just pay what I need and get one, that I most likely will never use. I think I'll first go into an LBS and check out what a new Dura Ace equipped bike goes for and the the $200+ or more for a hub to sit on the shelf won't hurt so much. Used hubs are a real crap shoot. But if it looks nice enough and the seller feedback is good enough.
I wish I had more extensive knowledge of exactly what works, but 25 years years ago I was still using 7400 and a freewheel. And these days I have a tough time remembering what I did 5 years ago.
I've never been a big fan of titanium freehub bodies; and you only gain about 15-20 grams. I swapped out my M950 freehub body with a Sora FH-3300 and packed the original one away. I'm pretty certain that you can use an M950 body on a 7700. The one caveat is to ALWAYS buy a complete hub since cones and dust seals might be different. Therefore since a FH-3300 fits an M950 which should fit a 7700, you could probably use a FH-3300 until you decide what to do. Grease and care in adjusting cones are your friend.
It may not be pretty, but here you go...
https://www.ebay.com/itm/38507440763...Bk9SR5zE5-qMYQ
John
Edit Added: And use some Phil's Tenacious oil in the freehub body before you install it.