It's time for me to contribute again.
Dave = Deve
A 1955 1st series 3100 has an open driveshaft. A 1954 and older 3100 has a closed driveshaft or torque tube.
My 1955 1st happens to be up on jackstands and I verified that mine is stamped N K 1004.
Look on the front of the rear axle, passenger side and at about 8 to 10 o'clock, there may be hand-stamped letters and numbers.
Cheverolet 1955 Specifications-Truck------Serial Numbers-----page 63
N = 1955 (J=52, L=53 etc.)
K = Factory location (K = Buffalo NY)
10 = October (Sept = 9 etc.)
04 = 4th day of the month
Deve's website said the torque tube for the 54 is different bolt-wise than previous years.
Setting NEW gears to mesh well is very important and if you lack the skill, I suggest searching for a rear axle shop near you.
Deep pockets are needed to purchase carrier/pinion and other bearings.
Factor that in if you also plan to go with a non-stock transmission i.e. S10 5 speed.
