The barcode sticker is how they are usually identfied, at least in the charts that I've seen.
Considering the way you obtained the tranny, and what the previous owner had indended to use it for, it possible that it is a combination of an S10 tailhousing/etc grafted onto a Camaro tranny.
As for getting a driveshaft, I would verify what you are going to need for length before you go spending any money on it. Measure whats in there center to center on the u-joints, compare the lengths of the trannys, and subtract the extra length of the T5 from the '57 driveshaft, and you should be really close. I can measure my Astro shaft when I get home tonight.
One other thing, the T5 has a snap ring about 3" or so from the end of the tailshaft. Remove this if you can. Its useless, and could cause problems should the yoke you end up using is longer/in closer than the factory setup forthe T5 was. You want to make sure that the driveshaft doesn't bottom out into the tranny before the rearend hits its full travel or you will break stuff.
