You would be looking at about $600 to add the PB kit and a new valve, that's doing the labor yourself...you will have to fabricate a mount for the new valve. If you do not "need" it know I would wait a little while and see if JD comes out with a kit.
Check with the folks at W.R. Long. They can provide the grapple and the diverter valve. You will have to order it through your dealer however. You can find them on the web at W.R.Long the 4N1 Bucket People.
I recently bought a 4120 and have been very satisfied. John deere is swapping to Yanmars in the 2014 Four series tractors. Also will be full tier 4 pollution controls. 4120 has only the interim tier 4 (less complicated)