|www.rodneybeede.com||"I would love to change the world, but they won't give me the source code" - unknown|
You are much better off if you made a backup of your original firmware. HTC doesn't offer an official download of the ROM besides the OTA update. I guess one could have intercepted that download while their original phone was downloading, but I didn't do that. Annoying that HTC doesn't just offer a RUU for each phone that you can download to your PC or even just a zip file ROM.
I had clockworkmod recovery so the RUU I found wouldn't work. I had to Google search for someone else's copy of the stock ROM. Trying to use clockworkmod recovery to apply the update would fail. Using a RUU also failed because the phone didn't want invalid signatures or older updates. fastboot flash system system.img also failed because that tool can't handle more than 200MB flashes (too large error).
What I did: