Well, let's see...

You won't need a spacer for 8-speed, that's only if you go with a 7-speed cassette. Which Dura-Ace hubs are they? If they're the newest 10-speed hubs, they may ONLY take a 10-speed Dura-Ace cassette. I found this out the hard way with a newer set of Roval wheels I have. The spline thickness is different, so you can't just put on a cheaper cassette. Very irritating, but again that's only with the 7800 series freehub body.

As for other compatibility issues, I don't see any. I suppose technically the 7400 chainrings won't work ideally with the newer narrow chains (9-speed or 10-speed), but I don't think you'll have any issues.

Instead of going friction shifters on 8 or 9-speed, can I suggest indexed downtube shifters? I had a full 7700 groupset on my bike with indexed 9-speed shifters and it was sublime (now Keith has the group). It was noticeably better than friction shifting.

Anyway, if you can clarify those few things, we can help you out

-Collin-