Drivetrain options for '70 GS455

[hockeyboyry]

Howdy.

I'm trying to get an idea of what kind of drivetrain I want to run in my car(1970 GS custom). I plan on doing a full frame off resto. I'm not going to bore you with my life story, so here are my goals: pleasant, smooth and easy to drive, while maintaing the "fun" factor with performance.

The main question I have is: What transmission/diff would achieve these goals? I was considering a 6 speed auto, or 4 speed auto.
I currently have:
-Buick 455
-TH400
-Unknown rear diff

I've been considering:
-6L80
-4L80e

Any information is good information. Thank you in advance for your advice!

 

[MelsRegal]

Why not 700R4 or 200R4 rather than deal with computerized transmissions in a car with no computer.

 

[LARRY70GS]

Back in 2006, I went with a Gear Vendors Overdrive,

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If I was doing it today, I would go with the 4L80E. That is a THM400 with a 4th gear OD and lock up converter. It will fit. Not sure about the 6L80E, although that would be really cool.