JD 400 was sorta a one of a kind tractor. Great tractor but did not share implements with any other tractor in the JD lineup. Of course if you get a 3 pt you can use Cat 0 attachments on it but mostly talking about the front attachments.
I had the opportunity to run one for a few minutes and I was impressed by it. There is a thread on here where someone replaced the engine with a 32 hp engine (it has plenyy of power stock).