The usual extra info on this series, for the Lamborghini Diablo SV, plus Miura and Countach...

There are 51 events (48 Trophy + 3 TT) with each car having a specific two-event showcase + TT.   The rewards 25-50-75-100% are split 8-13-18-28GC, with only the  Diablo able to be upgraded enough to complete the series.

You can reach 75% with the Miura alone, in my case just scraped in missing a couple of upgrades(PR38.7 and some not management!)...

...and obviously the same would apply with just the Countach upgraded to that PR.  With both fully upgraded you would get to 88%.

Note that the final race is PR48.5 not PR48.8 as stated in the patch notes, which should save 70GC on those costs of upgrading the Diablo enough, e.g.  omitting the outlined final Tires&Wheels in this chart as usual courtesy of Paulo over on Facebook RR3 Trackside: