Jacko,
You raise a good deal of issues in discussing the use of the Mk1 Merlin. I myself would like to know the detailed answers to the various questions that you raise.
I guess that we won't need more lift in Iraq because soon we'll be out of there. w.r.t the Afghanistan; the amphib lift would be a bit pointless so the naval mod's eg fold etc, won't matter ashore.
If we assume that there are excess Mk1. To re-role they would need clearing of their ADAS (SONAR), 903/903A (SONICS) and Sonobuoy Dispenser + any other excess seats/racking (as you say, a role fit, although the lad's and lasses at Culdrose may disagree!). Load lifting is limited - they don't have the same cargo hook or lift frame; no DAS;no armour seating; no SF or Air/Gnd comms; no Sat Comms; no NVG; no ramp; excess Mission System equipment. All in all a very significant mod package to convert the Mk1 to a really useful capability that can defend itself from manpads and the like. i'm not saying it can't be done but would expect it to be at least 6 months to a year design + 6 months Trials/Integration testing + 6 months to mod the aircraft (dependingon how many you need). Plus, is the Merlin cleared to operate over 43 degrees?
You refer to the Mk1 in Telic. To my knowledge they didn't have DAS, Air to Gnd comms, Sat Phone, medium load lift capability; this wouldn't be much use in Afghanistan right now.
Also, I expect an aircrew type person would offer comment on the ability to generate the crews; considering the potential mod time, it should be feasible.
Other options to lease or upgrade Puma a would, I hazard, be achievable quicker than the Mk1 option.
PS - i wouldn't bet on recovering Mk6 for Carson, more like spare Mk4, this will keep the mod pacakge for theatre entry bits and bobs to a minimum - but don't know for sure, just guessing.
Also, I think Stn 290 and 243 ring a bell, but you need a current jungly AEO to give you the definitive answer.