Yes, in hindsight, a link to that tech document in my original post would have been very useful. I'll try to improve my future posts with that in mind

thanks, I'll try to track one of those spacers down.

I managed to find my post where I documented some of my findings re: Shimano freehubs. You can read it here: https://www.bikeforums.net/showthread...ht=shimano+hub

I have more detailed notes somewhere but who knows how long it will take me to find them. Regardless, I note in that thread that the freehub spacer was identical between an RSX hub and an Ultegra 6500 hub. I swapped the freehub body on that RSX hub for one from a Tiagra hub so I'm certain that I have an extra freehub spacer in my parts bin. If you can't track one down, let me know. Should only cost a postage stamp to mail to you.

does a 105 hub of that era use the same spacer? I have one of those sitting around with a blown out velocity synergy waiting for a new rim

Based on what I've seen I'd bet a good beer on that 105 hub using the exact same spacer as the Ultegra. I'll try to dig my spare spacer out in a bit to give you measurements from which you can confirm that you have the correct spacer on hand.

Freehub spacer dimensions: 29.25mm O.D., 22.75mm I.D., 1mm thick

Shimano doesn't call it a spacer, they call it a washer. I fits in a grove behind the freehub body seal (if it has one).