The spacers dont have to be exact. All there for is so you dont run out of thread with your castle nut. I used 3 1/8 thick 5/8 washers and no problems and I run the car in autocross competitions.
I, too, tried to install the newer style ball joints with my spindles. However, I had previously installed (some time ago) new Moog or TRW (can't remember which) ball joints which were actually OVERSIZE. We had a hard time putting them in, too. They made the holes in the control arms too big to hold the SN95 ball joint in there.