What cam should I get?

Hello. That Comp Cams XE268 is too big for your 273 in my opinion. Duration at .050 is.224\.230. The Comp Cams high engery 268 has 218\218 degrees of duration at .050. It shouid give you the idle sound you are looking for but will be down on power on the high end due to the low .454 lift. You could use 1.6 ratio rockers and get a .484 lift. That sounds pretty close to what you need. My 273 had 09\14 duration at .050 and .458\ 470 lift at 1.5. It had a stock idle but worked well. Look at Hughes racing tech articles on how to size a cam. Good luck, Bob