When I got my project Vespa GS 150 it came without some of the original parts. One part in particular is the glass fuel tap. Mine had the typical large frame fuel tap that is available at any scooter parts store. I have recently been on the hunt and I have come close but still do not have the original yet.
The large frame fuel tap from Motorsport Scooters
Here is another shot I got from an GS150 restoration I saw at 2nd Avenue Scooters. Also the "DELLORTO SEREGNO ITALIA" lettering on the tap.
These are the tap I bought from ebay and scoot.net both are not correct for a GS150. The glass one on the left is what you typically might find on most 1960's Vespa scooters but not correct for the GS150.
Notice the glass tap on the left and how the fuel line goes to the right. On the GS150 tap in the pictures above all the taps have the line goto the left.