Chevrolet Repair: incorrect slip yoke?, full size chevy, piece drive shaft

Question
wayne.
  i have a 1971 chev van(beauville) w/a 125"WB.
it has a 307 V8 and standard transmission.
there's a 2 piece drive shaft system w/a center bearing.
  i replaced the original longer drive shaft years ago with one from a full size chevy car.(the original shaft fell off and was lost)
at once i noticed the yoke would not align in phase with the front shaft assembly.now i have a drive line vibration that eats my rear universal joint once every 2 years.
 whats the differance in the slip yoke from a van verses a car?
 if there is, what would be the correct yoke for my van.
                thanks in advance
                  barry  

Answer
Hey,

Sorry for the delay but I have been rolling this around in my cranium today and just want to get a couple of things straight:

: You still have a two piece driveshaft right? A full sized chev car doesnt have a two piece and most singles are not long enough unless they are modified so you must have a single on the back of the hanger bearing now.  Cadillacs used double careden joints back then but to my recollection that was the only odd shaft.

Phasing is of utmost importance when it comes to driveshaft vibrations.  Another thing that can contribute to it is driveshaft angles.  A worn out motor mount and or trans mount can put undue stress on the shaft if the angle is too great.
 make sure that the slip yoke still has travel.  Is it binding when you put the vehicle on the ground?  Also make sure the slip yoke is very free to a point you can slide it with one hand but not loose to a point you can hold one half and move the other rotationally.  about 060 would be too much. Incorrect pre-load on the pinion bearing can cause some slop as well.  
 I think concentrating on the travel of the slip yoke would be a good idea.  If the splines fit and don't bind you are good to go.

Wayne