4-Speed DB Manual Box for the Rapide

Does anyone know if the 4-speed manual David Brown gear-box used on the Lagonda 3.0 litre cars from 1954 through to 1958, is also the same 4-speed manual box used in a few Rapides in 1961-63.

I believe that there were two types, a simple plain gear box casting used from ca. 1954-57, and a latter one, used on the last cars made in ca. 1958, with a ribbed casing

Or is the Rapide / DB4 gear box, an updated Mk2 box, with same gear ratio’s inside, but external outer case more ribbed and strengthened ?