I'm at 50% and about to put the car in for repairs but I'm wondering if I need to buy the Body, Brakes and / or Tires & Wheels level 2 GC upgrades to finish this series.

They are 12, 10 and 12 GC respectively.

My car is currently 7/27 for a PR of 44.7 after the first round of R$ upgrades and is 5 hours away from finishing the 4 R$ upgrades in the next round.

So far the only PR requirement I've noticed is the 45.0 minimum required to run Le Mans in 5.3.