"its converted to 12v already.
he just needs a ballast resistor correct? and of course 12v lights, volt reducer for heater blower,ect?."
Assuming he wants to convert his 6 volt truck to 12 volts that should work. However he could get a 6 volt coil and a 6 volt 235 flywheel and 6 volt starter and retain the original 6 volt configuration. Of course a ballast resistor would not be necessary if the ignition was upgraded to a pertronics electronic ignition. IMHO the pertronics is the way to go because the new point sets are garbage.
"are the rear ends the same? i mean, his torque tube is going to bolt up to the 53 4 speed, correct?"
That depends on weather or not his truck had a 3 speed or 4 speed.
"will the 56 third member swap work with the 51 gmc rear,if he wants to do that?"
Yes, however the pivot mounts on the axle will need to be welded solid, or better yet cut off and replaced with new spring perches. That is assuming the axle in the truck is the original 1951 1/2 ton axle.
