'Does the 'J' have the legs and the role equipment to fill the gap left by the retirement of the 'K'..?'
Err, yes. Outside of the SF role (in which the K continues) and the lone aircraft in the Falklands, the K has done little meaningful tasking for a number of years due to a lack of airframes, the bulk of C130 tasking having been done by the J. The J is now in the Falklands & while it may not have the External tanks it seems to be coping & may get them yet.
When I flew Ks the external tanks were only of so much use - they add weight even before you fill them with fuel, which reduces the load you can carry, particularly when it's hot/ high which is where most of the job is now. Don't recall filling them up much when we flew around the Middle East so they were only so much dead weight.
The J has been here for a decade, and doing a fine job.