For what it's worth, I had an '87 1000 and an '88 1200 and both of them had the mounting tab as shown in ExPrez's photo. These were the bonded aluminum models; the 1000 had a steel fork and the 1200 had an aluminum one. My son is still riding the 1000 but the 1200 had a crack in the downtube at the junction with the (cast) headtube and had to be put down. When I replaced the crankset on the 1000 with a compact crankset, I had to use an adapter band instead of the tab because the slot in the tab wouldn't allow the derailer to be mounted low enough. I gave the tab to someone on Bike Forums; the tab that was on the 1200 got lost somewhere. When I tried later to find another tab I was unsuccessful. However, Nova Cycle Supply has this part:

http://www.cycle-frames.com/bicycle-...R-WELDING.html

which could be drilled for attachment to the threaded holes in your seat tube.

Good luck!

Bob P.