If the seller has managed to have a good conversation with Jeff Lindsay about this bike, then full marks to him as I've been told that Lindsay isn't fond of reminiscing about the old days.
However there are some oddities about the listing that I wouldn't expect:
This is a 1991 frame offered for sale with a Z1 fork, which is described as a 130mm. For your $5,850 you don't actually get a view of what fork you're getting, but what the hell I suppose. If you have to ask, you can't afford it. My guess would be that it's an earlier 100mm fork from around 1998 or 99, it doesn't look like the earliest Z1s.
Even if so, it's still about 9cm longer than the rigid fork that the frame was designed for. He says the head angle is 70 degrees, but if it was designed to be 70, it must be about 65 with the Z1 on it, which is a full-out downhilling angle. I assume the Z1 wasn't fitted because the owner wanted to go downhilling, so perhaps the most likely explanation is that he wanted to make it unpleasant to ride, as being the best way of preserving it unused.
However the seller also says that the original rigid fork has never been used, as it was replaced with the Z1 after purchase. Is a bit of history missing here? Was it preserved as a display bike between 1991 and 98 and only then sold? Seems slightly unlikely as Mountain Goat folded at the end of 95 and Jeff Lindsay severed all connections with the mtb world when Altitude Cycles closed down in 96.
Finally the frame weight is quoted at 7lbs 10oz. What might this mean? A 5lb frame with 2lbs 10 oz of paint on it? Could the never-used rigid fork be part of that weight? So is it a 5lb frame with a 2lb fork and 10oz of paint? Maybe we're getting there. So it's a not very light frame, a not very light fork and a hell of a lot of paint.
Seems to me this is a work of art, no more designed to be ridden as a mountain bike than the Mona Lisa was. And with the Z1 fitted as a bizarre twist, just to confirm that you wouldn't actually ride this thing. But excellent though the paintwork is, you can get serious works of art for $5,850 and this is just a nice bike made unusable by the precious paint on it.