I'm not an owner, but sometimes owners don't frequent the board enough for a quick reply, so I'll tell you what I know.
1. Talking to local dealers, I've been told that all post bans have the fix (the pre-bans can be fixed by Bushmaster as well). I've had some people indicate that some post bans come with extended mag wells, but I can't confirm this yet.
2. Kurt's will install the under-rail, amongst other modifications. I don't know if he provides the forward grip or not. Parapyropig sent photos of his, so hopefully he can provide that info. Kurts address...
3. Kurt's again. But another user suggested this link, and I plan to inquire on whether or not these monster muzzle brakes can be installed on an M17 barrel. Link...
Again, I hope pyro (or Kurt) replies. Pyro has some impressive photos of his highly-modified M17s. His set up inspired my search for one. I barely missed a great deal on one from this site... I'm still in the market for a good deal.