Suggestions for Rear End Build & going to 200R4 from TH400
 

My father had a 71 GTO and drove it into the mid-1980’s. He put 114,000 miles on in it as a daily driver. I have the car and finally restoring it as a driver so I can enjoy it.
I’m using a guy here in CT to re-do the rear end. He asked what brand of internals I wanted to use. Any suggestions would be helpful. I’m keeping the 3.23 gears and thinking of going with a 200R4 trans that he will also rebuild. Car will be driven but not raced. Motor was done already with mild improvements by Jim Taylor(R.I.P.) back in 1998-ish.

Looking for suggestions for what brand to use for internals for rear end rebuild. Also, any advice on what it takes to replace a TH400 with a 200R4?

The 200R4 is about the same length as a 350 or ST300 so your driveshaft will be real close but not exact and may need to be shortened, some folks say that they can use the 400 driveshaft while others say no. The crossmember can typically be reused with minimal modifications. You’ll need a new shifter cable and potentially shifter or at least modified shifter if using the factory one, Shiftworks is the go to for cable and modified OE shifters.

https://shiftworks.com/collections/gto-lemans-products

Now my real question is why? My ‘72 with a M20 and factory 3:23’s is fine on the highway up to about 70-75 mph, I’m not sure that adding an overdrive is worth it unless you’re stepping up to 3:55’s or higher IMO.

I agree with 67Lemons on the ratio. 3.55 or 3.73 would be the better choice