It was a well trodden path from the N Sea to an airliner in the mid 80s.
I can't help you with the process now, it was an abridged course or sufficient P1 fixed wing hours, a fixed wing twin IR, a GFT ( 2 in fact instrument and GH) and a few ground exams (performance, variable pitch props, air con and P of F ).
Bottom line in practical terms is that an experienced multi crew Helicopter IR pilot can transition quite easily. It was not unknown for a pilot with 2 years N Sea experience to be flying passengers ( with a training captain) with only 15hours multi engine fixed wing time.
The fixed wing market is buoyant at the moment so do it now.