If you're using the external slave cylinder, you need to make sure you have the spacer/bracket for the slave.
You also need to have the clutch pivot 'T-nut' which clips into the fork and allows it to pivot on a bolt (called the pivot)
PN for the T-nut: 13-86-149-001
PN for the bolt: 13-86-183-004
PN for the fork: 13-86-596-004
PN for the bracket/spacer: 13-86-172-002
Here is a diagram; you're interested in B8, B9, B10 and B-13. In the picture, 9 & 10 are reversed but the part numbers are correct.
All the above part numbers are current Tremec (TTC) numbers. I can get you the GM numbers if you need them.