The Dallas Morning News recently started an aviation blog (welcome to the blogosphere), and I thought you might be interested in reading this recent post.
In addition to the 727s mentioned, we also flew a single 727 in 1978 that was leased from Braniff as part of a law suit settlement. The lease period was to have been two years, but we returned the aircraft early. The Airways Classics that I did on Southwest last year has an interview with Captain Mark Clayton who flew our 727s.
The Morning News post also mentions the Lockheed Electras that Air Southwest (our original name) intended to operate, and here is the proposed livery: