Criminy!
The CMP is doing the best they can. I have been 100% satisfied with all of my dealings with CMP over the years. You're not buying a new rifle. You're buying a rifle that someone used before you, most likely in a war. And $400 for an M1 is a great value. The parts alone are worth that much.
If you get one that is unserviceable, rather than bitching out the CMP over it, it's a much better practice to call them and let them know the problem. I've never heard of them not fixing the problem and even throwing something else nice in there for you. By sending your rifle back with a nastygram, you screwed yourself, hoss.
Heck, I had an unservicable trigger group on a rifle. It was a zero stage trigger and just unsafe. I called them and got a whole new trigger group for my rifle. A few minutes with some pin punches and it was all fixed right up and I even had spare parts left over.
CMP has some of the best customer service ever. Period.
There aren't any M14s to convert. We're out of M14s. Anyone who believes there will ever be M14s needs to get off the crack pipe. All of the M14s went to Lithuania, Latvia, Bosnia, surrendered to Captain Crunch under the Clinton administration, or are in current use by our military. You'll never be able to buy one at any price from CMP. You can occasionally find one that is a machinegun or a converted NM rifle that made it through to private ownership back in the day, but you can expect to pay a pretty penny for it.
Once the M1s are gone, they're gone forever.
In the future, CMP may offer ARs. They have in the past for club sales, but I don't expect Congress to let them sell ARs for private ownership...
ETA: It doesn't matter the M14s are machineguns by BATF since they don't exist anymore, and darn it, that's post # 666.