I totally agree with Hogwild. If there is a question as to legal or illegal, I would always slide toward the legal side. No sense putting yourself in a position of being a fugitive...no one here is a lawyer (your lawyer) as previously mentioned, and this would surely end up in court. That can get expensive, to say the least. I don't feel like ending up on a BATF watch list.
And as many have pointed out here, once in the TC game, you will no dobut want a cabine and a pistol when you get older, as there are places you may want to go where hunting with a pistol just isn't allowed....like Canada for big whitetails.
I fully intend to get another pistol and set it up as a carbine...probably buy my brother-in-laws .270 carbine when he sells it, as I plan to do the Canada thing myself in the future when finances allow it.
But I have a question....if I buy a pistol and convert it to a carbine, can my underaged child (under 21 yrs of age) hunt with it....realizing that it is registered as a pistol?