I raced there (Eagle River) with Pro Vintage for the first time in 1999.
We raced on Friday during the day and had (I think) 3 exhibition classes that ran with the Friday Night Under the Lights show.
I think there was also 1 or 2 classes that ran during the Sunday part of the WC show.
I'm pretty sure PVR was racing there in 1997.
Side note.......Back in these years they had to be an actual "Super Modified" type chassis 1973 or older (Starfire, Blizzard, Thunder Jet ETC) but even back then we had Wilwood master cylinders, Mikuni carburetors, Whal Skids and deep "v" aluminum skis.
I remember asking Terry Purvis if I could run 1974 SnoPro glass on a 1973 Starfire and he said no. I asked why not, he looked at me and said (I'll NEVER forget this), "Roger, do you really want to be here when there are 400 entries"? He and the others that started PVR were very visionary!