I think the 1974 USAC-mod is actually not a rF2-mod but an AMS-mod.
It was developed by the admins running HSO from about 2015 till late 2019. They then switched to ISO (International Simracing Organisation) where they organize races with AMS as a simulator.
All the info ref the 1974 USAC-mod can be found on their forum.
Hope this helps,
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