Is this kit only for the TwinTurbo manual Z or will it fit all of the Z32 models?
This brace has been tested on Right Hand Drive 91 TT manual. It will not fit the LHD (American Market) Z32's.

Why didn't you make it from steel for extra strength?
If you bend this brace, you have likely already broken something on the other side of the firewall. This brace is stronger than it needs to be.

How tight a fit does it need to have against the master cylinder?
Adjust the bolt so that it is finger tight against the master cylinder, then add 1/4 turn. Tighten the jam nut so the setting won't change. You do not need to overtighten either the bolt or the jam nut.