73 Duster going from manual to automatic

Yes I know. WHY??? Well my wife and kids would like to drive this once in awhile so an automatic it is for now.
I have a 73 duster with a 225 manual on the floor. I will be putting a 400hp 71 360 in it. I also have a 76 duster 318 automatic as a donor. What other than a balanced 360 B&M flex plate should I be considering. Thank you in advance.