Recommended posi rear end?

hope im in the right place in the forum. trying to compile a list of needs for my 70 Dart. i have a /6 right now but will eventually swap in a 340 or more likely 360 (cheaper....jus a 18yr old guy). so was wondering, what posi rear end would you guys recomend for me? ive heard maybe 8 1/4 suregrip? honestly ive no idea. keep in mind, the car is gonna be a daily driver, so street gears :toothy10: thanks!