Markvb, Pedro Gorosabel is definitely from Eibar. Nothing Italian about the name either. He would have been Pietro and not Pedro,

The PG before the serial# is the give away as to the manufacturer.
This proofmark is surely present:

and it is a Spanish proof.

I believe the 850kgs are proof pressure.

Here you can find a list of Spanish manufacturers and their proofs:
http://personales.jet.es/rafa/b_punzones.html
P.G. - L.G. are for Pedro Gorosabel

JC(AL)

"...it is always advisable to perceive clearly our ignorance."ť Charles Darwin