Sergio Scaglietti producerd couple different spyder designs for Ferrari.
First of them was based on Alfredo Ferrari idea for a damaged and rebuilt 166 MM/53 s/n 0050M (renumbered from 0308M). This was later modified and saw usage on all sorts of sports racing cars.
The second design was called the ‘pontoon fender’ spyder, as it had channels behind front wheels for air to cool the drum brakes. The first time this body was used was on the Ferrari 250 Mozna s/n 0432M rebodied by Scaglietti in 1957 on order from Luigi Chinetti. This might the the precursor to the style used also on later, November 1957, Ferrari 250 Testa Rossa.

1957-bodied Ferrari 250 Monza

1957 Ferrari 250 TR