360 to replace 273

Enjoy the increase in power, if your old rear end is a 7 1/4 you might consider the 8 1/4 or 8 3/4 unless you go very easy with your right foot. The old 7 1/4 will take "some" abuse but not a whole lot. Like I said if you go easy the 7 1/4 should last a while...mine did(5 years). The 8 1/4 I have now is much more fun, I can even abuse it if I want.