Yes it can be done to a Silvia with a few mods, namely the the big pin from a 5-lug S14 must be installed into the arm of an S13 (the S14 arm is longer than the S13). This enables the use of the 5-lug spindle and maybe strut on an S13.
The biggest rotor and caliper I've seen on an S13 are a JZ Supra 330mm rotor and Lexus SC430 monoblock aluminum 4 piston caliper. Bracket was custom and caliper was modified.
For a 240Z, the hub is way different from even an S13. I think Mike SCCA tried Z32 calipers and the mounting ears were a different size and or the mounting ears had to be ground down. The conclusion was that it was not worth the effort, do a search on this.
If all you want is 5-lug on an early Z, use the Z31 hub and some lightweight Wildwood or Outlaw calipers. You also need a spacer (different for 4 and 5 lug) Z31 rotors.
I switched from Z31 4 lug to Z31 5 lug and kept the Toyota calipers. That reminds me, I need to sell those 4 lug spacers and rotors...
Owen