Historical evolution of SCCA Sports FRacing classes

I am on a research path trying to define the evolution of the SCCA Sports Racing classes through the years .
Engine displacements being most significant from the transition of the initial Modified classes to Sports Racing and when that all happened.
Mid-Late 1960's there was A-B-C-D-E-F-G-H Sports Racing.
Those classes morphed in A-B-C-D around 1967-68 I believe.
I believe the Modifieds were renamed Sports Racing after the 1965 season.
And there was C-D-E-F-G-H modifieds, as well as a short lived I Modified from 1958-1961.
There must be people in the sports racing community who have this data, probably in their heads !
Interested in understanding exactly how we got from eight [8] Sports Racing classes to the P1 and P2 cars of today.
Any sports racing historians out there ?
I have the equivalent in open wheel classes, partly because I have lived it, but now am curious as to my fendered brethren.