Hi Montage,
My work colleague and I have been working on converting an old steel frame, 58cm, into a single speed commuter. Alas, we've diverted most of our funds to our own bikes so its not been paid full attention but is pretty much all complete.
However, he is willing to sell the frame with brake calipers, unless you want the whole bike, for pretty much what he paid for, £35. Ill see if I can upload pictures on here unless you want me to email them to you.
The rear drop out is currently 130mm, but being its a steel frame, it can be cold-forged into 120mm am sure.
It is quite heavy, well, by my super light bikes standards, but we have nicked named it The Beast!