Ok, are you aware of the limitations of Dura Ace 7400. It’s 7 speed Uniglide, although with a bit of work you can fit HG cogs, you need a threaded cog that screws on to the hub. Replacements are expensive. Replacing or removing the freehub requires a special tool which if you can find one will probably cost an eye watering amount.
I bought a 7400 complete group set including hubs when it first came out. Hubs still spinning fantastically some 27 or 28 years later. Luckily I bought more Uniglide cogs at the time and expect the locking cog you can turn the others around to get some more life out of them.
So if you have everything to make your new hub work, enjoy it!