I have rebuilt the front end on my 1970 Cutlass Supreme, new ball joints, bushings, and changed out my spindles from Drum brakes to Disc. My question is the castle nuts when tightened are too short for the cotter pin to engage. Are there taller nuts or should I put washers under the nuts?

 

Are you talking about the nuts on the ball joint studs? The studs should not be sticking up that far. Either you have incorrect parts or the tapered holes in the spindle are egged out. Either way, stop and figure out exactly what is wrong. It is mandatory that the ball joint studs wedge in the spindle holes. Where did you get the spindles and the ball joints? I'll note that I once got brand new ball joints for my 62 from Kanter and the studs were machined undersized. Took me a little while to figure that out. They did send me new ones that were correct.

 

here is the kit I bought from Andersen restorations and a pic of a lower ball joint

 

Where did you get the spindles?
Did you carefully measure the tapers on the old and new ball joints? That's how I found mine were machined incorrectly.

 

Spindles I bought here. And I never thought to measure the new spindles.

 

I've had a bunch of tie rod ends from various manufacturers with the same problem. Quality control has gone to crap.