I recently just got a 98 ZR2 rear end it has the bigger U-Joint, my blazer has the smaller.
Will my 96 blazer Yoke fit on my new Zr2 axle?

I dont want to start the change until i have all the parts and this piece is in question.

 

I don't believe so. They make conversion u-joints for this type of application.

This thread explains it well:
ZR2 rear end in a non Z

 

Thanks I found what I was looking for.
the U joint is a Saginaw 44 and a Spicer 1350 put together which equals=
Part Number 2-1153