Hummmm,,
I flew in the 1975 Nats and it looked like ALL ST 35CRC to me. At that time the law of the land was "stock plain bearing throttled engines".
I assembled a Mongoose with one of those Fox Carrier Specials for the local hobby dealer and it just didn't work. That's not to say the others didn't work. Spotty quality was a Fox standard, at least until the Mark III Combat & beyond.
Actual results, scores & engines used from 1975 Nat's:
Jr. 1st place 378.15 STC35
Sr. 1st place 394.20 Fox .36PC, and Sr. 2nd place 361.90 McCoy-Testor .35
Op. 1st Place 394.12 STC35, 2nd place 392.60 STC35
All plain bearing engines, NO modifications allowed, and all winning entries in all PC classes got torn down and fully inspected for any modifications.
Note the Jr. & Sr. scores exceed the 3rd place Op. scores and beyond. ACTUALLY....the Sr. score of 394.20 with a Fox.36PC was the highest score of all combined; Jr, Sr, and Op.
This was when entries numbered into the high 60 or more count (some years +90), and Jr. & Sr. flights outscored Op. scores. Will never see this occurrence again...