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.