Help Identifying Duster Rear End

Hi,
I've been on the search for months for info on what rearend I have in my 71 Duster. Has 340 and is originally a V8 car. Looking to upgrade gears. I daily drive it and do car shows. planning to run it next season in a few club races. I think I'm close but wanted your professional opinion. I'm fairly handy and know a few people that I could do the work with and learn something new.
Thanks for the help!
Images attached.