I did my own. My distributer came with 36* mechanical advance. I welded up the windows in the advance arms and reground them for 16* and 20*. I adjusted my advance rate by bending the tab that holds one end of the big spring. With less preload on the big spring I get total advance by about 2400rpm's with the stock springs. There is a window in the breaker plate that allows you to adjust the spring tabs w/o disassembling the distributer. There is a great write up here http://reincarnation-automotive.com/Duraspark_distributor_recurve_instructions_index.html on DIY. I think the owner of the site does rebuild and recurves as well.
I did it the same way. My Duraspark had too wide advance slots, so I welded them up and filed them back into shape, but with smaller slots. Then I adjusted the advance rate with different springs.
BR Motorsports Ignitioneering can rebuild it better than new and recurve it. You can google them if interested as I don't have their URL handy. 1-800-328-3333.
I know those guys, sort of. It's mostly sprint car stuff. They got in the ignition business because sprint cars used to use magnetos and they need attention.