one possible research avenue -

as you mentioned lygie information is a bit sparse. one interesting path you might pursue would be to check on rizzato's better known marque for the period of your machine. one possible place to start could be that page at cr. have a look at the metal of the professional model and see how it compares with yours.

it may prove that the metal was the same for the two lines from top to bottom or it may turn out that they are different...

perchance a bit o' fun in any event.