Here's a Diamondback I just acquired... S/N 8917290. It is an Expert TG. It is OS Cro-Mo tubing. RX100, indexed 7sp downtubes. It is white top/black bottom with paint splatters. I got it from the original owner, he said it was purchased in early 1990, so it should be 89-90.
I will try to get some pics late next week when I get some time.