No way no how will you get the 4 speed transmission out with the transmission attached... unless you remove the cab.
Drop the transmission and remove the engine and bellhousing as an assembly.
The 3600 is a 3/4 ton. It should have a HO52 Eaton rear end. Most likely the gears are 4.56:1, however 5.14:1 was an option. The best you can do with that rear is 4.11:1 from a 67-72 3/4 ton with an automatic.
