md 600 driver ....
Errrr ... IF the OP wants to do SP IFR (in ANY Helicopter) then he need to be certified and so does the machine ... the days of IMC ops OCTA are long gone ... thus the assumption is he will need an appropriately configured machine ... I know the standard machines are only certified for VFR flight ... I did not say any different ... I just pointed out that there WAS a SA341G Stretched Gazelle that WAS certified by the FAA for SP IFR flight that means it was APPROVED, CERTIFIED and thus would have had a Flight Manual Supplement to allow same .... thus you are not quite correct.
The OP also asked if there were any IF experienced pilots that had flown both types ... so I responded as I had flown both types IFR ... what did I say that was incorrect ?