Wolfgang Hearter at Columbia car and cycle has some parts for these old fuel taps such as the ally float bowl nut. If you didn't get them with your bike it's not looking good. I wonder if anything could be done with the Guzzi straight down exit taps like your Laverda ones Disco Volante sell. Could they be modified to take the nut? You would then have to make the perspex float bowl and pot metal spigot yourself
Below is a bad pic of an Orlandi Tornado tap with Wolfgang's float bowl nut, the spigot and the old, perished float bowl glass. I've been trying to find time to fix these for years but the Laverda copies work well enough so they are still on the bike. I can supply any dimensions, the main problem for me is the sealing washers, I'm making some wad punches for this but can't find cheap 1mm or less viton rubber sheet. The nitrile I get just swells in modern fuels - any suggestions?
Spark plugs are B6ES / B7ES. Cosmo were selling the CW240L pinks for a while so I bought some and didn't notice any difference but my machine could do with a tune up anyway.
Let us know how you get on.