I would not advise plain glass/Perspex David: you'll get an atrocious beam pattern. The original glasses for both Lucas and Bosch lamps were especially designed to match the reflectors, the glasses having a "pattern" which was actually a series of prisms, each refracting the light and the whole giving the total beam pattern.
For one of my Aurelia B20s, I tried Lucas reflectors/halogen lamps mated to the original Carello glasses and the beam patterns were awful (possibly the reflector's focal length was incorrect for the glasses?).
When I was trying to complete my Augusta many years ago, I couldn't find any Bosch lamps for sale and the originals were tatty and incomplete, so I bought a pair of very similar Carellos in Italy. These are of FIAT origin - Ardita or possibly Ballila and are slightly larger than the Bosch lamps. I've welded up the sidelamp tell-tales and adapted the shells to fit the Bosch/Lancia pedestals, then fitted 6V halogen lamps which, together with beefed up cable sizes and earth returns, give excellent lighting.