please help 225/318 swap

hey world im new to this and want to swap my 225 slant 6 to a 318 i bought from a guy.The 318 is from a 68 charger and will be going into my 72 swinger.Any help you could give me would be appriciated :sad2: .This is my first mopar and am just learning.
I have
225
a904
7 1/4 ? rearend