Robert McNamara backed the project to replace the original 2-seater Thunderbird ('Little Bird') with a bigger 4-seater Thunderbird ('Square Bird') for launch as a 1958 model, and George W. Walker oversaw the design by the team bof Joe Oros. The 'Square Bird' grew 11-inches in wheelbase and 20-inches in length to provide a full four-seater vehicle. The extended roofline of the Thunderbird was given by Elwood Engel and passed on to many contemporary Fords including Falcons, Galaxies and the Mustang. Ford gave their new Thunderbird a unibody construction which allowed a very low height, albeit with an intrusive transmission tunnel down the centre of the car. There were two engines, the 5.8-litre 352 FE V8 and the 7.0-litre 430 V8. Ford launched the 'Square Bird' in Spring 1958, much later than most 1958 models, and it was offered as a 4-seater hardtop or a 4-seater convertible and 37,800 cars were sold in this shortened year. Slight trim and grille changes were made for the 1959 model, revised rear suspension and the addition of the larger 430 V8, and sales increased to 67,400. There were modest revisions for 1960, and an increase in sales to 92,800 before the 'Square Bird' was pensioned off for the 1961 'Bullet Birds'.