I wanted to reduce the noise and the paper embossing on my Sears Medalist Electric 12 without recovering the platen.  This should work on many Smith Corona electrics.  This changes the gear ratios and slows the power roll.  It's possible to make it so slow that the keys make a faint impression when the shift is enabled. 
Remove the body and belts.  Remove the small bolt/washer/felt that holds the double pulley in place.  Hold the large side of the double pulley in a padded vise and use a parallel jaw pliers to pinch the two sides closer together.  Use a spacer of your devising if you want to have precise width. 

Take the pulley out of the vise and insert a screwdriver between the two haves of the small pulley sides.  Gently twist the screwdriver to force the pulley halves apart.  It's easy to see your progress and control the amount of spread. 




Reinstall the parts and give it a try before you put the body back on.  It's possible to make the large pulley too narrow and the small pulley so wide that the belt will drop too far into the vee and get caught in the parallel sides of the pulley stalling the machine.  It's easy enough to push them back together and then peen bushing that the pulleys are on to hold it in if you go too far.  The picture below shows how my belts ride in the pulleys.  It's still possible to use the copy set knob with this setup.