1936 chevy pickup, pro's help me out!

Is this truck being restored?  Unless there is some desire to keep it stock (and if you are glassing an enclosure into the dash, my guess is it is not intended to be stock) I suggest it should be converted to a 12V system.  This is not a small job, and will require wholesale replacement of the wiring system.  But both for adding a stereo and for future replacemnts of things like headlights, going to 12 volts is the best thing to do if at all possible.

If, however, there is a desire to keep the rest of the truck at 6 volts, use an antique car voltage booster: http://www.antiqueautomobileradio.com/power.htm  You'll have to use a relatively low power head unit to stay within the current ratings.

A lot of charging system back then were 6 volt pos ground, Not NEG. ground. Also the generator only put out a MAX of 24 amps. Unless it has been change. It's not really to hard to change over to 12 Volts NEG. ground. First find a 12 volt chevy generator. A red tag generator would work great (1958-1962 Chevrolet) also would fit the OG. 216 ci engine, change the voltage regalator and ad a 12 volt coil, you might have to ad a ballast resister to the coil. Leave the starter and points in the Distibutor as is. Change all the light bulbs, run a  resisters to the gas gauge. Ad a voltage drop to the radio, or change it out for a hidden modern small system.  That's it. I hope this helps.

Julian59