Problem w/ the GCR weight is that it will bery difficult to get a 280ZX to that number.
Other problem is that the ZX was severely de-rated in power, compared to the 280Z.
130 vs 170, in order to deal w/ emissions.
Don't know if you can monkey w/ the ECU enough to get that 40 hp back. Some of the reduction may have been in the cam.
The brakes are an attractive feature but the power is not.
I've raced 280Z's for a long time and have never seen a 280ZX on the track.
Another negative is that parts are getting hard to find - both for suspension upgrade and general maintenance. Nissan no longer supports the 240-280 cars much. A few dealers try to help.
Think hard about this.
Bill