r154 and w58 do have slip yokes, and guess what, the inside of that slip yoke is SPLINED! they fit the splines on the out put of the trans,and yes they ARE diff for w58 and r154. if you dont beleive me i can take you to my storage unit and set an r154 on the ground right next to a w58 and can hand you a drive shaft for both and you can try it yourself and you will see that they are in fact diff. and you can measure their lengths if you like. the r154 is 2in longer.