Driveline help needed! Rearend swap -

Yup, if you went from a 7 1/4 to an 8 3/4 you will have to shorten and balance the shaft. Insert the slip yoke into the trans until it bottoms out. Pull it back an inch and see what the difference is.

I would suggest you find a local shop and call them and ask exactly what they want for measurements. Some shops will want one thing while others will want it done a different way. Whatever the case you will want the suspension loaded.

You will damage the transmission if you leave it like it is. I had mine cut, balanced and they installed my u joints and cleaned and painted it for 90 bucks.