one thing to point out-
i can say from experience that the bolt-on gear shifters are really poor and don't usually work that well. you are much, much better off fabricating your own.
i've done a few setups, back when i was involved with racing.
attached is some pictures of a set i had handy.
as you can see, this uses Lambretta parts, mostly series 2.
the fork clamp is a series 2 one that has been put in a lathe and had one side made flat, to bolt to the aluminum plates.
the bars were 15 degree bent ones... i believe off a BMW.
the shifter bits are series 2 lambretta, because they can take a standard, easy to find Vespa lever. the were turned shorter, then had bronze bushes installed inside them to make them fit on, and turn smoothly on the bars.
there was a stop brazed on the bars to keep the shifter in place o nthe end of the bars.
the shift rod has a bronze washer between the flat bit on the end and the end of the bars.
the shift rod rides i na steel tube that has been brazed into the bars at the end and also where it comes out of the bend of the bars.
the rod has been shortened and drilled to take a series 3 servetta - style aluminum shifter pulley held in place by a roll pin.
the cable stop plate is brazed on to the bars and is half of the bit from inside a 1965 VNB vespa.
the handlebar mounting bits were i think some sort of harley spacer or mounting something my father picked up we modified to work. i don't remember the details exactly on those.
beyond that, it's mostly off the shelf.
the kill and headlight hi-low switch is an old 60's British bike part.
the little mount next to the switch was for a bicycle computer for a speedometer.
magura master cylidner for the hydraulic brake, althoguh i had a cable perch on it at one time.
i think the throttle assembly is a tommaselli dirtbike one, and the headlight is a rubber worklight for an agricultural application that i put a smallframe bulb holder assembly into instead of the sealed beam floodlight it came with.
for what it's worth, ti worked very, very well. the shifter assembly was put together with grease about ten years ago and the weight of the lever rotates it down when the cables are unattached, even after all these years.