Back when I was a spotter at Birmingham BEA were just replacing their Viscounts with 1-11's and Aer Lingus ditto with 737s.
Until there's a good 1-11 for XPlane this 'what-if' livery fills the gap - imagine that British Airways had a 'legacy' BEA livery for one of their first 737s, just like they have today on an A319.
There are a few minor glitches, the wings are mirrored so we get too many registrations, don't look too closely at the extra letters :)