Lindsay purchased surplus P-51s (mostly P-51D) and began a restoration process. They would strip out all the military equipment, add a second seat behind the pilot, add extra fuel capacity (some models), update the avionics, install a tall tail like the P-51H, plush out the interior to provide the most comfort possible and finish the job with a civilian paint scheme.

One of the P-51s main attributes was its great range. The first P-51 conversion, named Cavalier, was in 1958. Orders trickled in for the first few years. The models offered were all relative to the range of the aircraft. The model numbers (all prefixed by "Cavalier") were 750, 1200, 1500, 2000 and 2500. The longest range Cavalier, the Cavalier 2500, included 110 gallon wingtip fuel tanks. Remember, with the second seat, the fuselage fuel tank was removed and the main wing tanks would yield about 180 gallons usable. Trans-Florida was renamed Cavalier Aircraft Corporation and purchased the rights of the P-51 design from North American Aviation. In 1967, the USAF contracted with Cavalier to produce the F-51D for export to South America under the Military Assistance Program (MAP). These aircraft were given new serial numbers starting with the first, 67-14862 and named "Mustang II". In 1967 a total of 9 were built. These aircraft went to Bolivia.

Cavalier also repaired and retrofitted existing P-51s that eventually went "down south". Several P-51s were sent to TFA (Trans Florida) from South America for repairs and upgrades.

Changes to the Mustang II were made for increased loads. The wing was strengthened to carry a total of 4,000 lbs of ordance and additional weapon hard points were installed, up to six under each wing. A rear seat was installed in these models, for observers. A new Merlin V-1650-7 was installed and these Cavaliers also received the taller H tail. In 1968, two of the new Mustang IIs went to the USAF as chase planes. These were serialed 68-15795 and 68-15796.

More orders placed in 1972 for 6 aircraft under MAP for export to Indonesia. The Mustang IIs did not have wingtip fuel tanks. With new ideas of how to keep the P-51 Mustang alive and in service, David Lindsay wanted to try replacing the long-standing workhorse Merlin V-12 with a turboprop. Lindsay perferred the Lycoming T-55 but had difficulties obtaining a copy. They were able to get a Rolls Royce Dart 510 Turboprop and installed it in civilian P-51 N6167U. This mod was not funded by the USAF, but by Cavalier.

The new modification was called the Turbo Mustang III. Cavalier tried to get the USAF and other air forces interested in the project but no sales were made. Later, Cavalier sold the project to Piper and it later became the PA-48 Enforcer. The Enforcer had little in common with the original P-51.

The USAF, under pressure from Congress, did order two prototype PA-48 from Piper. No other orders were place and the project died. The two PA-48 Enforcers do exist today at USAF Museums. Many Cavalier Mustangs are still airworthy today.