I beleive it is the old "Kent" 4 cyl Ford that is a "pushrod" design.
It is not actually "approved"--it is the only motor that came in the US version of the car as imported between 1978 and 1980. Accordingly, it is all you can use in IT.
In the UK, the Fiesta had all versions (displacements) of the Kent, the CVH (Escort engine) and even the ZETEC in the last incarnations. There were also TURBO CVH versions scooting around.
Good car.