Hopefully you have an AMC patteren Turbo 400. A Chevy or any other T400 won't bolt to the AMC block. Adapters can make it possible, but it's unneccesary since AMC T400's are easy to find. CJ's and full size Jeeps which had autos up to 1979 had the T400. If you have the right tranny you're going to need to adapt the tailshaft for the transfer case. The Jeep T400 almost exclusively had the Quadratrac tcase behind it. You definitely don't want to swap your Dana 300 out for the qtrac. Novak can set you up with the right adapter to bolt the 300 up to the 400. www.novak-adapt.com
The 400 is quite a bit longer than your T5, so you're probably going to need new driveshafts. Your rear one will be too long and the front will be too short since the transfer case will be closer to the rear axle. Both existing shafts can be retubed or you can buy new ones.