Demojob
You keep refering to a bellhousing as a separate part.
A separate bellhousing is the part that contains the clutch, & bolts to the front face of a gearbox case. The only thing a bellhousing does is to mount the box & contain the clutch & it's control components.

Are you calling the gearbox case, complete with it's integral bellhousing by the name "bellhousing", or is there something i'm missing here. I have not seen a separate bellhousing for these models yet, only separate gearbox cases with integral bellhousings.

My parts book calls it "transmission case"

An adapter plate is usually found between the cylinder block & the bellhousing, or the block & the gearbox, however, my parts book refers to the plate at the rear of the transmission case "Assembly, Plate Adapter" so adapter plate it is, although i would have regarded it as the rear bearing support plate.
Chris
P.S.
Prodat, i think that, from your description, that the "extention housing" broke, but bloody hell, what did you do to it to achieve that.