What Lambretta/Vespa models are similar?
Following are the similar styles so you can figure out what parts might fit your scooter. We can't know all the differences on all the models, but the following will help. Any corrections to be made, let us know.
For further assistance, see scooterhelp.com serial numbers, and browse by model.
Lambrettas are easy. You have Series 3, Series 2, Series 1, and LD types, then a few early minibike-like models. All S3 share - or at least can fit - most other S3 model parts, only the body styling or the engine configuration is a little different. Even S1 and S2 share many parts with a S3.
Vespas are complicated because there are many different models to begin, then many that overlap in different ways, so maybe no/some/many parts are interchangeable between models. (Fortunately, some models are the same but simply 125cc vs. 150cc.) Then there are country-specific variations with different VIN numbers (UK Douglas, French ACMA, USA Allstate); for those you have to figure out your equivalent Italian model noted below.