Perhaps the most significant point about the lunar-orbit flight proposed for Apollo 8 was that the command and service modules would fly the same route to the moon as would be used for the actual lunar landing.
An ‘A’ type mission would be flown with a Saturn V and be used to test the Launch vehicle, spacecraft, and a high velocity lunar return. Nasa cover the ‘A’ mission with Apollo 4 & 6.
A ‘B’ type mission would be flow with a Saturn IB and test the lunar module development, and propulsion, and launch vehicle staging. This was accomplished with Apollo 5.
A ‘C’ type mission would be flown with a Saturn IB and test the command and service module and evaluate the crew performance in low earth orbit. This was accomplished with Apollo 7…
Since the lunar module would fly only in space (earth orbit and lunar vicinity), the designers could ignore the aerodynamic streamlining demanded by earth’s atmosphere and build the first true manned spacecraft, designed solely for operating in the spatial vacuum.
The mode that Apollo would use to land on the moon was the most studied, analyzed, and debated decision made for the lunar landing program. There were four main choices Direct-ascent, Earth-Orbit Rendezvous, Lunar-Orbit Rendezvous, and Lunar Surface Rendezvous.