follow-up on your questions:
1. I cut the ugly parts off for asthetic reasons. I didn't measure the clearance on existing brake bridge, you may be able to leave it in place and just grind a bit off the underside to create the mnumum clearance. You need ~12.25" from the center of the axle to the underside of the bridge to clear a 520 rim with 1" road tire fitted.

2. I folded the rear triangle due to running an 8-speed chain on a single speed set-up with less than perfect chainline. The misfit caused the chain to occassionally attempt to ride up on the top of the gear teeth as if it were going through a shift. The absence of a chain slack mechanism means this is like taking a prybar to the rearend, then when it snaps back, it's like a hammer. I learned this the hardway as the frame folded on me during an agressive climb. Would be nice to report that it was just due to my overwhelming strength, but the real truth is that the damage was already done, I just didn't know it.
Now I ride with a proper chain and also an automatic chain tensioning device called a derailleur.

As far as surgery is concerned. I cut and fit the parts using the same tools you probably have in your shop. I had a friend with no cycling experience and no particular interest in working on frames, but who did have a gas bottle and a torch. The brazing is not much more difficult than soldering a plumbing connection. You can read up on what you need to know and be an educated novice to get the basic alterations done. I butt connected my new chainstays with an internal backing sleeves. the small gaps and brazing flux allow the brass material to flow with just moderate heat. The internal sleeves also provide additional strength to the tubing where the material properties have changed due to heating.

Good lucK. the Retreau Guy