needing a new rear end and advice

i have a 1972 plymouth scamp was a slant 6 car paid someone to put a 318 in it. but now i have cash again and i wanna upgrade the rear end as its still the slant one what should i go with and what all do i need ( like will i need a bigger or stronger drive shaft

is it a stock 318? planning on putting sticky tires on it and heading to the track? if not i'd leave the 7 1/4 in it.