I have the 1999-2000 Rallye tanks. They are the low tanks that look like bulging sidecover/saddlebags (linky to pics of one here)
. They're not the Heck tanks that straddle the rear fender.
I bought them from a guy in Europe who bought them for his Adventure. After finding out how hard they were going to be to fit, he decided to sell them. That's how I got them.
Those double seat stays that are on the early Adventure subframe are exactly what is in the way of the tanks. One of them has to be cut out, the other modified. After that, there were subframe tubes that went below the tanks to where the passenger footpeg mounts are. It ain't gonna' be easy. In fact, I'd bet that a high-pipe LC4 subframe would be an easier starting point. It doesn't much matter because I have the facilities to make a whole new subframe if necessary. I just don't want to.