Because machine guns are so expensive, because of the long delay in getting ATF approval of the transaction, and because of the fraud that's been cropping up in this segment of the gun world, I would say that a personal inspection of the gun is almost mandatory. Even if you have to travel half the length of the country to see it. I suppose, in a pinch, if the seller is well known, you might be able to get by with really good pictures.
If the gun is at least 50 years old, it might be worth getting a C&R FFL so that it can be shipped directly to you from out of state. This could save you dealer transfer fees as well as time. (A Form 4 is still required.)
The larger question is whether this is a wise move financially. I personally would answer no, but then I'm jaded because I bought my MG's back when they could be had for hundreds instead of thousands of dollars.