Overdrive

[rollin68]

I'm running a C4 tranny with 3.55 gears, i want better freeway rpms so I'm converting to an overdrive. My friend's brother has a overdrive with a computer he was gonna stick in his 66. Now my question is, what is the computer for(shift electricly?) and how much harder will it be to install. Also, he is selling it all for $600, is that too much?

I know i dont have many details, but i wanna know what im gettin into before i get too deep. Any info is helpful on converting to an overdrive. Thanks

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68 fastback modified 289, C4, 3.55 gears, 2 chamber flomaster, GT look-a-like, lowered,
blue head lights, blue blinkers, blue side makers, blue turn indicaters on hood, blue interior lights, blue map lights, blue liscense plate light, blue back-up lights(rewired the blink with the blinkers), blue alarm light, and blue strobe light attached to the front 1 1/8" sway bar