Can you look very carefully at the bottom edge of the skirt? It may have some numbers relating to size or model number. It looks like an early Borgo. Can you also measure the size of the piston at the skirt area? It is probably 78.0MM or a slight oversize from that. I may have some old ones.
look in the inner side of the piston most of piston producer named their pistons .
Think its an 1600 Borgo or Asso , but Mahle also possible. Seldom with 2 rings.
Possible the 2-ring borgo for 1300 with modified dome for reduce compression ratio.
Have some in my collection, but with other dome designe.
The motor is preperated by Conrero what is told me.
The height from the center of the piston pin to the top is 50,5mm.
The height from the center of the piston pin to the bottom of the lower piston ring is 14,9mm.
The height of the lower ring is 4,5mm.
Distans between the rings is 3,7mm.
The height of the top ring is 1,5mm-
The height from the center of the piston pin to the top of the area on top of the upper ring is 31mm.
Hope this is ok fore idetificeation of the piston.