Sounds like someone has been at it already, with the mismatched parts. Doesn't matter, excellent all-around frameset, use whatever parts work.

The 7-sp model came as both the Lemans and the Lemans RS with the smoked purple fade (aka Purple Haze).
The group was Light Action and had white vinyl-tipped shifters, white accents on the FD and RD. Wheels should have been bronze Araya's. The Tange 2 frame was 87-89, but '89 got the unicrown fork.

Not always worth the cost of a repaint, but a media blast and powder-coat could be affordable depending on your location. Here, it's about $75, but I generally strip first with aircraft stripper from Walmart just to be on the safe side.

Choose whatever color you want, and then choose decals.

The DT decals in that style are available from VeloCals, in either a white or black lettering.
The top tube decals are NOT available that I know of, anywhere, but the VeloCals kit comes with other graphics you can put on there. The kit includes small "Centurion" decals (miniatures of the DT decals) for the seat stays, and an optional set of the "squiggle" graphics in the same size, which could be suitable for the top tube.

You can clearcoat over the decals, using hobby clear or an $8 can of Duplicolor from an auto parts store. If you have the frame and decals only, you can clear the entire frame, which works pretty well and protects the decals. Given the durability of powder coat and the decals, however, clear coat is not required. JR likes to offer his 1ml thick vinyl over the decals, but I prefer to leave that off.