Rear End

When you add up all that you are spending on the 318, you will find out that if you spend the same amount on a 360 you will get a lot more power. but we are dealing with a 318 so with all your add ons, my opinion is that an 8 1/4 rear will suffice for you. Your esult will not be big power so the more affordable 8 1/4 should do fine.
for your personal reference: 7.25--max 175-200 HP
8.25--max 350-400 HP
8.75--max 550-650 HP
This is my opinion...

PS Mopar drive shafts are strong, you will not need a new one just have it cut I believe it is 1.5" for the 8.25 rear. I still run the slant 6 drive shaft with my 360 and it never said boo, just make your U-joints are good ones. I run 255/60R 15 but with an open rear.