Read the part about the mount. Original was made to isolate frame flex from the Cab. It was still held in place so it the Cab would not "tilt or move around". New mounting on a modern frame would I think would only require some rubber pads to prevent squeaks. On the slightly newer Cab the center mount in the back was changed to 2 one on each side. Cab floor to the frame rail. Look at the shop manual for 54 to see.
47 Cab mount:http://chevy.oldcarmanualproject.com/shop/1947truck/47ctsm0101.htm
Good reading.


Steve H