welcome to the shop Joe - if you've got yerself a 55 2nd series [no V8 in a 55 1st series] then the next investment you should make is a
shop manual, as well as the
owners manual [glove box book] and the assembly manual
the standard rear gears in any 1/2T 55.2 were the 3.90:1 with either the column shift 3 speed or the floor shift 4 speed - with the optional 3 spd over drive trans the rear ratio was 4.11 - that was what ya got up until 58 when they started offering an "economy" ratio, 3.38:1
Bill