Originally Posted by
icemilkcoffee
There are many generations of Dura Ace and Ultegra/600 hubs. Which generation specifically are you talking about? The FH7400 one cannot be updated with a different freehub body. The FH620X, on the other hand, might be- at least from the Shimano drawings it looks to have the same interface as later HG freehub bodies.
Yes, the mount interface is similar but depth/thickness of the freehub body needs to be similar, if not the freehub body will 'stick-out & add too much width to the drive side. This will cause poor dishing of the wheel.
The Shimano Ti bodies have a thicker 'rear' and require a hub shell that accepts that. The Ti bodies are similar to the 4400 below, or deeper for some XTRs. As mentioned earlier, 7700 Ti body may fit on a 6500 (which is similar to the 4400).
As noted earlier, the few Shimano aluminum bodies used a different mount type. Don't know if anyone else used the common Shimano body/shell interface (like the FH-62??), and if aluminum was ever done. Most of the aluminum bodies by other makers use pawls on the body & ratchet in the hub shell (similar to the FH-7800, which is a unique design for Shimano).