Christian, I know there is some gap yet to be filled (in between the Appia, which stopped production in 1963, and the Grecav Eke, and somewhere in between there is yet another secret probably kept by a panel van...) but there are at least 3 different pins in this kind of latch. The Grecav pin is fatter at the bottom and and will not seat as deeply as the Mangusta pin. The Mangusta pin tapers at 20mm length.
for example, the Grecav plastic latch is 17mm opening at top, 20mm thick and 12mm at bottom (so a 7' angle). Nate and Denis helped, the Goose pin is more like a 9' angle.
Asking every Italian ebayer with Appia parts 
, a picture showing what seems to be an 8mm thread and 14mm diameter pin (vs. another mystery car, with more like 17mm diameter and a 10mm thread, as the Goose) below. Note also the similar lathe marks on between the Goose pin and the mystery pin on the right.
Finally, the fit on the Goose seems to be a match between the rubber bumper on the engine cover matching the recess of the pin. Note about 10mm spacing using what are probably 10mm "small OD" washers (at 18mm diameter)--so the stackup of washers is tuned by measuring the recess of the latch pin and then adding the height of the rubber bumper next to the pin.
Damn, we're close...btw, I haven't found a Lancia part that was used exactly on the Goose (close but no cigar on everything I thought was right before, for example Fulvia sun visors...!) Lee
