Hello Chris
Water outlet elbow 31-450 sold by Cavalitto
Radiator cap: I have seen quite a few different types, mostly screw-on. I think the original was bayonet and Cavalitto sells them, but by the part number it's Aprilia.
In your case, if the female tread is still useable, have a cap with the corresponding tread made (from brass)
On my radiator, it looks as a brass tread was soldered onto the original opening a long time ago.
Be aware, Cavalitto is expensive. If you want to order, I suggest to select the articles on the web-site
https://www.oldlanciaspares.com and order by e-mail: info@lanciricambi.it
However if you want a quote, go by the Web-site.
Interesting the dynamo you have fitted. can you give us information on it, perhaps a picture, thanks very much
Karl