The conversion, if you are already a helicopter crewman, starts with 3 months at SARTU (RAF Valley) and builds up from winching over the golf course, through drums, wets and decks, to long(ish) cable cliff winching (sits).
The OCU course at St. Mawgan is around 6 months, depending on the weather, and builds on the skills learned at Valley.
There is also pre-employment Basic Immediate Emergency Care training with the Army near Aldershot, giving you Ambulance Technician skills (and a little bit more).
The extended IEC training is the advanced medical skills training, after which you will be a registered paramedic. This tends to be about 18 months after arriving on the flight.
As has already been said through, get in touch with one of the flights.