I've been restoring a bike back to gears that was converted to a fixie. When I got it, someone had painted it (poorly) and removed all decals and other identifying info. The frame has two numbers imprinted on it:

Driveside rear dropout - G1283 (possibly G1288)
Left rear dropout - 8067340

So I know from this that it is a Giant-made frame from '83 or '88, but beyond that, I'm at a loss. I thought it was a Schwinn for a long time, but when repainting it I discovered a small heart-shaped braze-on underneath the downtube, towards the headtube. I know this is a common feature that kept downtube shifters from sliding, but I've yet to hear of Schwinns from '83 or '88 having these.

Here's some other info -

1.) Quill stem (labeled "83L" for the odd .833" sizing)
2.) 26.6 mm seatpost
3.) Square tapered bottom bracket with plastic dust cover
4.) Rear Brake cable guides on top of top tube
5.) Lugged frame
6.) Only one set of water bottle bosses

Most likely original parts left on -

1.) Weinmann alloy rims
2.) Sakae "Randnner" Road Champion bars
3.) Sakae CX cranks
4.) Dia-Compe sidepull brakes

That's all that I've got. Thanks in advance for your help!