The Brabham BT20 was made by ISI and is continued by Studio-397. It's available in the Steam Workshop, as are many vehicles and tracks. Look through there. You may find more that interests you than I've noted here. Just click the "Subscribe" button, and the item will be downloaded and installed. At this point, I'm not sure what's downloaded and installed when you first get rF2.
Ferrari 312-67: https://forum.studio...312-1967.57827/ is available in the Steam Workshop.
The "Eve" (Matra) and "Spark" (Tecno) cars are included in the Workshop as Eve Historics 1968 and Spark Historics 1968. When you subscribe you get F1, F2, and F3 cars. The Matra V-12 F1 1968 is also in the Workshop as "Eve Matra F1". The Porsche 917k is also in the Workshop. The F1 1975 cars are in the Workshop with a League Edition (all cars equal, but different bodies and liveries) and the Historic Edition in which each car and livery has individual physics.
BTW when you log into Steam, search for me as JIMMYC and request I add you as a "Friend" then you can look at my "Favorites" in the Workshop and go from there.