about engine swap

i am new to mopars so i have a question about an engine swap. i recently purchased a 72 valiant with a slant six and an auto trans. i would like to put a small block in it. i want a 340 cause i hear thats the way to go, whats advantages and disadvantages between a 340 and a 360. what exaclty do i have to get and do to do this swap? what tranny do i need and wheres a good place to look for parts..any info that u all could give me will really help, thanks alot....glenn