need help with upgrading my 8 1/4 rear end.!

Thanks in advance for any help. This will be my first rear end work I have done and I need help upgrading my 8 1/4 rear end. 1972 Duster was a slant six and now putting in a 340. I know every loves the 8 3/4 rears but my 8 1 /4 is already in the car and I've heard and seen a lot of people running the 8 1/4. It's only going to by street cruising and car shows and having some fun. Probably no drags. I just don't know where or what to get the stuff to upgrade this rear end. Anything will help from where to get the stuff and what all to get and gear ratio? I'm pretty new to choosing gears and all that. Thank you so much for any help or links for place to get stuff from.