The current JD 3000-4000 machines have a circular cut-out on the underside of the hood (maybe the 2000 series, too).
Owner's have the option of buying the exhaust pipe and the edging material (cover the hole) for their dealer and installing the vertical exhaust themselves.
Does the hood on your 4210 have the hole-thru option? If not, you may need to install a side-panel exhaust pipe. Similar to the type on the older 50 and 70 JD CUT's.
Give your dealer a call and see what they recommend.
AKfish