"I should also amend my statement that the V 12 (type 117) was dropped into a 750 Monza chassis. That's wrong.  The 750 Monza used a tipo 510 chassis. The V 12 Monza came
earlier and used a tipo 504 chassis. It was a 2400 mm deDion five speed set up.  The main tubes are round and 64 mm and 50 mm in diameter. Used only in the four V 12 Monzas.

I do not know how it differed from the tipo 510 except that they were 2250 mm and later had coil spring front suspension. All the early Monzas had transverse leaf front
suspension (V12 and I4).