I purchased a set of seats for my 74 RC from a Military guy in San Antonio who had a Mid 70's RC that he did a full Late Model Hemi swap into his truck. It was awesome and he said it drove great too.
This was before there was any aftermarket support for late model hemi swaps and he had close to 10K into the late model swap. I think he used a late model transmission too. I'm not sure what transfer case he used, but his front differential was still on the passenger side.
Just looking thru my emails, I still have his email. But I bought those seats back in January 2010.
I know that Brutal Offroad in Bandera has done a lot of late model hemi swaps in our old tin grille's. They've got the recipe.