1928-E29 were acorn or bullet-shape cadmium-plated steel, with fluted lenses. 1929-31 were hemispherical stainless with "Twolite" logo, "bullhorn" lenses. Both lenses 8" diameter. Earlier reflector sockets were centered, single-bulb. Twolite reflectors were offset 1/16" for their different bulb geometry and available as two-bulb (no cowl lamps) or single-bulb (with cowl lamps). The AA trucks were all painted steel, I believe.
The vendors carry accurate replacements, at least for the Twolight type.