V8X5M is a Vespa engine prefix/VIN code.

V8X5M is engine VIN number for 80cc engine used in PK80s, PK80s Elestart vespa models made through years 1982 - 1986.
P.S. This engine VIN number is for the engine block/casing and it doesn't mean that over the years and even accross the models there isn't slight modifications of this engine parts, their sizes or even internals.