...and here's the info for this, the last of the three new car series which also use existing cars...

Cars: Lamborghini Countach, Ferrari F40, Jaguar XJ220
Events: 42 (39 Trophy + 3 TT)
GC Progress Rewards: 7 / 12 / 16 / 25
Highest PR Required: PR57

75% comes around Tier 17, PR48/49, so you can reach this with a reasonably well upgraded F40, and indeed a fully upgraded F40 (PR59.1) exceeds the highest requirement.
If you have this, then when Jaguar Legacy Part 2 arrives, you'll only need to upgrade the XJ220 as much as you need to to get through.

I got to the end without servicing either my Lambo or [fully upped] Ferrari