The J is fitted for but not necessarily with externals. The USMC and and the Italians for example had theirs delivered with tanks. We being the RAF knew much better didn't. Now we're paying loads to get them retrofitted
and, as yer man says, we've got one knocking about already.
Wiring up externals on the J is a little more involved than just slapping them on as they have to be wired to interface with the 1553 databus. The tanks off the K are no use to the J.