Hi Mike,
This page may give you some idea of the work involved and the amount of paint damage to be expected in brazing on a derailleur hanger.
http://www.yellowjersey.org/
On the subject bike I note that the top tube rear brake cable eyes are still in place. The bottom bracket cable guides, if removed, leaves several options, a clamp on guide, brazing on new guides with the inherent paint damage, or probably the simplest, using an under the bottom bracket routing with a plastic guide plate.
The chainstays have been painted black which makes adding back a brazed on cablestop fairly easy as paint matching is not a problem. Just make sure you decide on shifter cable routing before doing this.
Spreading the rear triangle can be done, but be aware that 10mm of spread takes a fair amount of bending (cold setting!) and brake bridges have been known to occassionally break free of the seat stays in such procedures. Following the spreading a realignment of the dropouts is recommended and it is a good idea to check the overall frame alignment too.
A fair bit of work that may, depending on your skills, require farming it out to frame specialist.
It is a nice looking frame, a shame what has happened to it, but it you can get it for the right price after factoring in the necessary rework, it should make an interesting project.
Marcus Coles
London, Ontario, Canada.