manual and auto transmission

[Koya]

I have the opportunity in getting a 1980 spider with a dead engine and auto, I am not concern about the engine being dead. I planned converting it to electric car, to my understanding having a manual would be better and more efficient. the question is: How much different is the diffrential of a car with manual versus to one with automatic. When converted the car will only be driven in second gear and maybe in third.

I guess the real question is: what affect one can experience if a manual trans is mated with a differential for automatic? I am new at this cars, my apologies for these basice question.

[So Cal Mark]

the manual cars had a 3.9 rear gear, the autos had a 3.58 so mating a manual with an auto rear results in slower acceleration and lower rpms at cruising speedsd