Many kits have been made for either small frame and large frame vespa and most of them are still in production almost unchanged.
There was also a period when it has been tried the twin induction way that should have been a big advantage over the standard single one, but this way was never really developped since the kit that adopted this solution  were just modified single induction kit already in production

In the market you have mainly two producers:

the big names are Polini, Malossi and once was also Pinasco.

The kit they sell are generally well made and reliable, expecially their alu kits.

Then you have small companies as Zirri and Fabrizi and very recently Parmakit, M1, and Falcracing at this time unfortunately only for smallframe as the Fabrizi. Since they don't target a very large public they can produce kits that are quite pushed and need more carefull set up to have an accettable reliability but still and fortunately they don't suffer the chronic piston seizures (at this time we can't say anything about the Falcracing since we don't have any experience with this one) of ' 85 - ' 89 RM125 Suzuki, the shattered pistons of ' 92 KX125 Kawasaki and they don't need to replace the piston kit every 15 hours as ' 97 - 2000 YZ125 Yamaha. But if you push them still further you will go very close to these figures.

FROM LEFT TO RIGHT: PINASCO 213 and PINASCO 130 TWIN INDUCTION (BOTH OUT OF PRODUCTION) and A RECENT FABRIZI 140 LONGSTROKE.