Its been awhile since I did one, but IIRC, you need the correct bellhousing, shifter, and a drive shaft spacer. You may also need to make minor adjustments with your cross-member as well.
If you go with a TKO 500 or 600, you will need to watch for the input and output shafts spline count. If the input shaft is 26 spline, you will need a 26 spline clutch (stock is 10). I believe all TKO 500/600's are 31 spline output, so you will also need a new drive-shaft slip yoke (stock is 28).