Last night I rode an old LI of mine. I was amazed at how good the rear brake was. When I sold it, the lad who test rode it for the buyer (who'd never seen a lambretta before) said it was the best he'd ever used. It was normal for me as it was my bike, but you get used to what you've got.
I did nothing really special with this brake. Makino 'race' shoes. GP cam. Decent quality cable.
BUT, the braking surface of the drum was in poor condition so I asked a mate to skim it in his lathe. This is what I suspect made the difference.
Just letting others know so they can try if they want.
I'm building a new bike at the moment and I'm going to rough the surface up with a dremel cutting disc. Hopefully it'll be the same.....or I'll scrap a brand new uni hub!