Jerry and Folks,
I've often pondered the same idea as to whether vintage lamps could be converted to LED. Typical LED bike lamps appear to consist of 3 main sub-assemblies; lens/reflector, LED circuit-board w/button-switch and battery (compartment). Depending on physical dimensions inside vintage bike lamp, it doesn't appear too difficult to custom rearrange these sub-assemblies to fit vintage housing. The one problem I haven't figured-out is how to provide for switch actuation without drilling a hole in the cherished vintage housing...perhaps a single remote (contact-closure) switch for both head and tail lamps?