The Life pictures show a round build date of 12/56, so I assume the launch took place in early 1957. Yes, the fins are clearly marked "AF 12". Your dimensions of the payload match up exactly with what I calculated, so they must be correct, right? I guess it's possible that there are two different Life photo shoots, but the payload section looks identical in all of them, and completely unlike anything in ROTW.
As far as the Cosmodrome kit, I loved building it, it ended up looking great, and it seems sturdy enough that I'm not afraid to fly it. The main changes I made during the build:
I didn't use the included bungee cords, and instead used twice the length of braided Kevlar
I extended the payload section to match the Life photos
I now had room to locate the altimeter in the actual payload section!
I used half-round plastic of the appropriate size instead of balsa for the conduits, which allowed me to route the wiring for sustainer ignition from the altimeter to the interstage area
I built the sensor shrouds out of styrene sheet, and moved them back to be entirely on the payload section, I didn't want to deal with part of the shroud and conduit being on the nosecone
I had Excelsior create beautiful decals that match the Life photos
Something to look out for: Since the sustainer fins are mostly over an area that includes the interstage coupler, only about the top third of the fin is "through the wall" and attached to the motor mount. As a result, on my first flight, I cracked a couple fillets on landing. I wish I would have done more to get those fins solidly attached to the air frame, maybe cut halfway through the air frame or something. I also plan on using a larger parachute in the sustainer, there is tons of room for recovery gear, but watch out for...
A change that I WISH I had made, would be to get rid of the steel cable shock cord mount. On my second launch the parachute got hung up on the cable eyelet and never made it out of the air frame. In the future I will make sure to push the cable down into the air frame (if possible?) so that the recovery gear is on top of the cable, instead of beside it. The sustainer would have been destroyed, but...
The sustainer motor didn't ignite
The booster motor deployed the booster parachute
The booster stayed attached to the sustainer
...and the whole thing tumbled down in one piece and landed without a scratch.
I guess I'd rather be lucky than good!