Got this cool box today too, its a shame someone added the handle to the top. It has the two brackets on the back where it fixes onto farming equipment. I bought it from a dealer from Shippensburg, Pa.
Its got a really cool latch on it too.

nice^^^

Here is an all original one.

http://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=farmall&th=899822