[Captainfab]

The '71-'86 K20 front rotors are 12.50" diameter, 1.29" thick, and 2.81" in overall height. The '99-'10 Express/Savana front rotors are 12.79" diameter, 1.50 thick, and 3.51" in overall height.

So yes they are a bit deeper, .70" to be exact. And they are slightly larger in diameter, and thicker as well. However you won't be able to use a D52 caliper on these, as they are just too thick. You would likely have to use the Express/Savana rear calipers, which may not be a bad thing, since I believe they are a dual piston caliper.

You might also be able to use the rear rotors and calipers for the Express/Sanvana. The rotors are 13.0" diameter, 1.40 thick and 3.42" in overall height.

This is the first that I've heard of using these rotors for a rear disc conversion of this type, so I don't know for sure if you could run 15" wheels without grinding these calipers also. Where did you hear/read about this?