In addition to Fred's comments the other option is Halogen. I don't know if there are any direct fit halogen bulbs for the older bayonet sockets but the bulbs are brighter -- and also run hotter. Sockets could probably be changed to a modern halogen version to use modern bulbs but the extra heat could be detrimental to the lens or enclosure.
Excellent grounds to the point of soldering on an extra wire to the light sockets and a clean connection on the sheetmetal to make the ground instead of relying on the original connections via mounting bolts and pot metal housings will go a long way toward making the original incandescent bulbs brighter. Having good clean wire terminal connections are also a given.
If you are interested in checking out Halogens, do a search to find some of the vendors. One or two mention base types on their offerings. For your original bulb base type you can go to Don's Bulbs
http://www.donsbulbs.com/cgi-bin/r/t.pl and enter your bulb number in the search field. On the page that comes up select a USA version to get all the base specs.
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