No expert, but looks like a jeep trailer to me. Missing the pintle ring of course, probably had the back cut into a tailgate? PM or e-mail MLUer Ian Fawbert he should be able to give Chapter and Verse as he has been setting up a trailer data base: Here
http://www.vintageengines.net/page11.htm
They do go for highly varied prices, oftimes not matching the condition.
Looks like you will be going for a drive?
Rich.