Number plates and air filters
I haven't bought an ally plate for a long time, but someone used to advertise in OBM. Ally and "custom" reflective plates are now described as "show plates" so that's what to look for. Show plates can be whatever size and lettering one wants (although ally plates are road legal on a vincent). "Road legal" plates otherwise have to be the standard british reflective billboard, 7 foot x 6 foot, an offence to the eye. 7" x 6" is good if, strictly speaking, illegal. Plod may notice, but hasn't so far.....
Someone in the US sells "as originally fitted for the US" - I think - Vokes filters for pre-monoblocs, and you might try a query on jtan. Otherwise, if you can ever get the bellmouths off the carbs, a K & N filter should be OK. If you get stuck I know who I can ask.