In 87 GMSM on page 4B-2 Rear Axle the picture shows part 33 designation on the LH & RH Yoke Axle Shafts
I would assume since both LH & RH are numbered the same, then ergo they are interchangeable.
But I'm not the best when assuming stuff.
HOWEVER, after sitting on this section I can see on 4B-11 a note about the lengths as 7.875" and 8.5" .
Model 36 and Model 44 respectively and they should have a metal tag c/w numbers.
I hope the above helps, diffs are not in my vocabulary .