You will want the 2" shaft.
Straight shafts do not have provisions for any wiper arm. The Universal clamp on mount arms are commonly used. To use an original style wiper arm you will have to machine the groove for the arm saddle and drill for the arm pin.
Tapered shafts allow the use of 1937-40 style arms with the retainer nut, which are cleaner looking than the clamp on arms.
There are 1941-48 spline adapters available for both straight and tapered shafts.
There are a variety of arm-blade connection styles. Make sure you get ones that are compatible and its a good idea to make sure you document what type so (hopefully) replacement blades will be available.
http://www.wescottsauto.com/WebCatal...3-34Closed.pdf