The usual extra info...
There are 54 events (52 Trophy + 2 TT) and the rewards 25-50-75-100% are split 7-11-15-23GC.  You will need both cars for 100% and only the NSX-R can be upgraded enough for the final two cup races.
For 75% you'll need one of the cars upgraded to PR31.7 or thereabouts, but if you already have the RX7 fully upgraded then you can do all but those last two cup races and the NSX-R Showcase and TT:

The NSX-R will cost 275GC to upgrade enough for the 100%.