The usual extra info on this series for the Brabham BT62, plus McLaren Senna and Lamborghini Aventador SVJ...
There are 57 events (54 Trophy + 3 TT) with each car having a specific two-event showcase + TT. The rewards 25-50-75-100% are split 9-15-21-32GC, with only the Brabham able to be upgraded enough to complete the series.
Any one car can reach 75% (and beyond) on its own if upgraded to around PR 79-80...in this case FU'd Lambo:
Thanks to Herdan upgrade costs for the Brabham can be found here - you'll need all but the final Drivetrain for 100% series complete.