Hey bergy,
I am with you there. The RPO Codes were only the offered items. However the 1969 Nova Specifications did include the 3.73, 4.10, 4.56, and the 4.88. I expect they were submitted with the AMA Specifications. They were just not shown on the October 15, 1968 version of the AMA as the L78 was not listed. I do not know if the government emissions certification would have been completed accordingly.
The copy of the
GM Archives 1969 Nova Model Specs may not be the final versions. But they do offer a few clues. But only a few as there is limited coverage of the 396.
This did have a copy of the Power Team Charts. But that chart did not go past a L48 with 3.55 ratio.
This also had one copy of the Vehicle Price Schedule which did include the L78. It lists the Standard Ratio for all L78 transmissions as 3.55. Nothing higher than that is on the this copy of the chart. So how would you know to write in the others?
Greg