Pantah

Glad you figured out a solution.

Here's something to keep in the back of your mind. I have actually encountered this same problem before where one side was not usable but the other was. Thankfully, the friend who owned the bike had another late 90's Cannondale which he had converted to a single speed so the downtube bosses were not being used. Again, that one also had one good side and one bad. So, take the parts off both bikes and make one good useful set. Worked like a charm.
Having a whole spare bike to rob parts off of isn't exactly a viable option for most people, however, if there's a local bike recyclery nearby, you can always check their supply of stuff and old frames. If there's a damaged Cannondale frame hanging somewhere, you could probably snag the bosses for dirt cheap or free.

The bike that got the good bosses installed is being being retired as it's lived a hard life and is beat to hell with a lot of damage. So, I do have a spare set lying around now. However, since I am a classic Cannondale enthusiast, I'm not inclined just yet to get rid of them. I might be convinced to though.