I'll get to the point. Do Chorus Ergo 2x9 brifters have to be used with:
1-Campy FD? If so, is there specificity on that, too?
2-Campy RD? If so, likewise above?
3-Campy cassette? If so, I'm assuming 9-sp only, correct?

Gracias, amigos y amigas

I don't have any 9-speed, so I don't know for sure, so I'm using logic & may be wrong:

1. I wouldn't think they'd have to be used with a specific Campy FD. I'm currently using Record Ergo 2x8 with an old C-Record FD. I imagine one could use pretty much any FD with Campy Ergo.

2. I'm not positive, but I think my brother is running Sachs Ergo 9 with a Campy RD. Or maybe it's the other way around. In any event, I think that if one were to want to mate a non-Campy RD with Campy Ergo, one would need a Shift Mate thingy, or possibly a Sachs RD.

3. you could probably get away with running a Shimano cassette if you used Campy spacers, if they'll fit. When I ran a Shimano cassette on my old SunTour XC Pro, I used SunTour spacers and it shifted beautifully. I would not have been able to do it the other way (Shimano spacers on a SunTour cassette), as the SunTour freehub body was of a larger diameter than the Shimano freehub body.

On the first two questions , I would guess you could run other than Campy successfully. On your third questions, I ran a Dura-ace 9 speed on my Campy 9 speed with no problems at all, just use a chain designed for the cassette. I am currently using a Shimano cassette on my new Chorus 10, and it works great.

I don't think the Shimano cassette will fit on a Campy splined hub.

I was figuring that he was wanting to run a wheel with a Shimano hub.

Any FD should work, because Campy has so many index points in its left-hand brifters that it is like having a friction shifter. This is a good thing. (Are you taking notes, Shimano?)

The right-hand brifters are designed to work only with Campy RD's and Campy cassettes. There is anough of a difference between Campy and Shimano rear cog spacing (and hence in the amount of cable the levers throw per shift) to make mixing and matching suboptimal without some sort of adaptation. But you can mix and match pretty much to your heart's content with one a Shiftmate. https://jtekengineering.com/shiftmate.htm

That's what I was looking for, exactly. Now my next question(s):
One of my bikes is running Shimano 600 STI's with an 8-speed Campy cassette, on Campy Vento wheels, and works great. Doesn't 130/8 and 130/9 equal the same amount in Japan and Italy?

If if were the French, I'd understand.

Or, is the freehub a different length Shimano vs. Camp?

And finally, if I need compatibility, can I modify my Chorus Ergos from 9 to 8?

From what I understand, yes. There's a part at the back of the body that pops out that contains the indexing unit (think Campy Synchro inserts, only different). Replace the one from your 9 with one from an 8. My brother switched all of his 8s to 9s about a year or so ago. I can check with him & see if he still has the 8s inserts lying around.

Thanks, I'll hit him up. I may not beat txvintage to it, for a Campy Ironman, but I don't mind being a close second.