Perfect mate thanks for that. One of the comments on that forum had me calling the FAA to confirm and it is correct.
With my verification letter from UK CAA the FAA will stick my 737 rating onto new FAA PPL with Private privileges and day VMC only. While this sounds useless initially, Southwest are recruiting and they require,
Certificates/Ratings: U.S. FAA Airline Transport Pilot Certificate. Unrestricted U.S. Type Rating on a B-737 not required for interview, but required for employment1. "B-737 CIRC.APCH.-VMC ONLY" limitation is accepted.
Therefore, once I do FAA written and FAA checkride on a light twin, that will drag that rating onto the FAA ATP.
Thanks for the help
VJW