336 is a pretty good all around ratio for the 8.2.With a Th-350 that will be a pretty good combo.
x2 on the Subframe connectors.. They will help prevent cracking the paint in the body line under the rear window. Add a good traction device and its all good.
If you an find a 12 bolt that they're not wanting a fortune for, thats a great choice. But the 8.2 can work pretty well if you upgrade the axles and use good parts.
I have a 68 also.. Sweet cars!