If you want to retain the '56 chevy tail light lenses
try to replace the bulb with an LED bulb. Should be much brighter. Use a red bulb. www.superbrightleds.com
handles a good selection of LED products. Just make sure the LED will fit the old socket.
Clean the old lens to remove oxidation etc.
Replacement tailights (lenses) should be DOT approved. In some States non DOT lighting will not pass inspection. Check it out.