I think that guy has his auction info a little confused. The E38 brake carriers have a wider bolting pattern, so they'd need custom carriers (which is what he says, right?)
It's easier to find a set of > mid '93 brembo 8 series 4 pots. Lots of people on the board have them. Mine are sitting in a box, else I might have some feedback
And then there's also the late E32 euro 4 pots, which I didn't know existed until a few weeks ago/a PM with Erich. They appear to have the same front caliper housings as the nurburgrings, and a four corner set went for ~ $300 on ebay.de recently.
That guy sells cool stuff, though. I'm still kicking myself for not getting the E34 rear power sunshade from him at the end of last year. Really hard to find, and I haven't had luck adapting the E32 units to the E34 parcel shelf...yet!
best, whit