If you only plan to marinise a handful of the 28 and save cost then why train up 2 RN sqns when the land SH element can be done by the existing crews from the RAF?
Because all that is certain is that there is an endorsed policy for Amphibious and CEC.....and an endorsed policy to transfer the Mk3 to the RN (and forget what the then ACAS had written into the SDSR book and CAS's SDSR briefing notes cos iit was fiction).