Overdrive or no overdrive?

[eddi]

Hi all, I have a 1970 Serie IIA and I am in the process of getting some work done. The restoration place strongly suggested I consider adding a Rovers North transfer case for $1,800 (parts and labor); their justification is that even over short distances it helps the engine by allowing it not to run as hot. I drive the rover every weekend, but I do not drive it over long distances often at all. I have to be honest, I am not familiar with the concept of an overdrive and therefore don't know if it is a good investment. I am already spending a significant amount, no where near a full restoration but still a pretty big dent in my pocketbook, and I am not sure whether I should go for it. Comments, ideas?? Thanks, Eddi[/align]