Couple tings, but first off. Sweet boxes.
1.) I'm 99% sure those belong to a member on here. I've seen those pics before. Actually that pic is on the collecting SO site. Which makes me wonder how recent and thus accurate the pics are of the actual boxes.
2.) Actually I'd be more interested in the other boxes the same person has listed for $550. Much more useable as a tool box. Again they belong to a member here.
3.) I'm pretty sure that is a later production of that box (early 40's say ~42?). Meaning it should (IIRC) have drawer slides and stops on the drawers. Which I think is a requirement for a using box.
4.) Something is up with the drawer pulls on the bottom most 2 drawers of the roll cab. I don't think they are original.
If you do buy it please post some pics. As for price. Yea I guess it is a fair price for that box. Just depends if you are a collector or a user? For a user you can no doubt get alot more workable box for your money. However the cool factor here is definitely higher than a more modern box. I actually have the top/bottom combo before that one (1937), and while it is cool, the useability is not that high. However I didn't pay much at all for it, so I'm content with the $/cool vs $/useable storage space. If you have the space, $ and ambition, maybe try a package deal for both sets? I'd much rather have the other stack than the one you posted. IMHO the other stack is much more usable, plus I really like those roll up front covers.
