The usual extra info on this series for the Porsche 935...
There are 42 events (36 Trophy + 6 TT) and the rewards 25-50-75-100% are split 8-13-18-28GC.   The LTS-winning PR65.9 is more than enough to reach 75%...

...but obviously you'll need to upgrade the car further to complete the series - the last cup race is PR68.5, which I gather needs an upgrade pattern of 5353333 (an extra 255GC spend).
#EDIT# abject apologies - that leaves you PR0.1 short - needs to be 5353343, another 95GC