47 and up 4 speeds are synchro, sounds like you have an early big truck 4 speed, they are non synchro granny low 4 speeds. I just yanked mine out cause double clutching is just like you said a PITB.
If you really do have an early 50s 4 speed, someone has already done the work and the saginaw will bolt in place. I've run a saginaw before and I like it as the up and downshifts are spaced nicely, but it won't gain you any on the top end and I just wouldn't be able to justify the shifter cost even though it is really nice.
Pictures might help.
