I can't say for sure what it is but I know what it isn't. They're definitely not M1 or M1A1 tubes. They're way too long for that and the back ends of the tubes don't look right at all to me. Check out this photo of (my own) M1A1 tube and you can see the differences:
I think they might be M-9 bazooka tubes with longer front ends added on. Look just past halfway down the outside of the tube, see the bulge? That looks a lot like the locking collar on a M-9 tube. Still, they might be something custom made with launcher parts. Clearly they're shooting M6A1 or A3 rockets, the same ones the ground bazookas fired. You can see the M83 shipping tubes lying on the ground. Take a good look at the third photo in the original post, note what he has his hands on, he's loading an M6A3 rocket. You can see the back end doesn't have pointy fins, it looks like an opened can. That's a later war A3 rocket.
That, along with the shape of these tubes, to me supports that this must be well into 1944 or possibly 45. It can't be earlier due to the type of rockets being loaded. They also could have shot the M-10 WP rocket for marking targets. Any of these would be wildly inaccurate given the ranges they had. The airplane would practically have to get within pistol range before they could hit anything with these.
Taylor, I say get some rocket pods built and get them mounted, it'd look most cool indeed, although I can't say what it'd do for drag in flight...