Just saying, I entered you topic for pure case.
I think that would be really hard to make 1.09 duels in the ways you proposed.
Isn't easy at all to find these old items and most of the current ones were used to spawn in 1.09 too, but with little differences.
So what, are you going to forbid a stormshield until somebody gets a 1.08 or a 1.08 one? Or whatever else...
But! But I find the idea interesting. Here in Europe we had (and few still have) rules about something similar to what you are aiming for.
It was called EP, that stends for Euro PvP. Just try to google ''diablo 2 ep rules'' and you will immediately spot some threads about that.
The rules are very complicate and detailed, but the purpose is interesting.
Us, as BvB community, we still apply similar rules on a specific kind of league called AoW. So, actually, in Europe you can
do BvB in three different ways: BM/pub way (that sucks, seriously), FFA rules (is free, just few smart restrictions), and AoW rules (way more restricted and fun).
So, my suggestion is to check these EP rules I was talking you about. I think you may find some good ideas for your league!

Good luck!