On my 55, the sockets were completely corroded away.  I had a couple
of the plastic "push in and twist" sockets from the tail lights on a
Niesen 200 SX.  I removed the old sockets, as I remember they were
rivited in, and then drilled a hole where the socket had been that was
big enough to get the round portion of the 200 SX socket through. 
Using a small file I cut a square notch for the portions of the
socket, that locks it in place, to slip through so the socket could be
inserted and twisted to lock in place.  Then I drilled a small hole
for a screw in the back of the light unit and attached the ground wire
from the socket to the back of the light unit.  Since the socket is
all plastic you need to provide this ground connection.  The standard
bulbs for the 55 fit with no problem and the lights are working great.
 I think I have seen these plastic sockets at several auto parts
stores, so obtaining them shouldn't be a problem.  The thickness of
the back of the Studebaker light unit is the same or close enough to
the thickness of modern car plastic units so they fit tight.
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Go to NAPA, Discount AutoParts, AutoZone or any parts store and in the 
'Help' line find the replacement park light/tail light sockets. You 
can get one that's all metal and snaps in from the back. Dont use 
one that goes in from the front (lens side), the bulb will be too 
close to the lens amd melt it. btdt 
cya jf