Would be great to have a thread for RSRs similar to the Ultimate ST thread.
I did notice there's not a lot of info here on those cars, which is why I've been adding my findings in my replica build thread.
I'm sure there's other cars (RSs maybe?) that were updated with (some of the) M491 options during the 1973 and 1974 seasons, but as the factory development during 1973 was focussed on the group 5 (prototype) factory cars, I know that some of the IMSA racers weren't allowed some of those modifications.
Anyway, looking forward to this! Hope and expect that people like Starkey & Hugh can add some info here.