5/7 drop question: What size tire could I run?

[TIMSPEED]

Could I run a 255/50 17 with a 5/7 drop? Right now, I'm running a 255/55 17 with a 3/5 and not having any rubbing issues at all. (Well, ok...ONE, but I don't think it's RUBBING, I think something else is hitting) But my rim is 9½" wide with a 5½" backspacing. Also, would I need to change my shocks? I'm running DT's both front and back. I think they told me the front's are basically stock replacement size, but the backs are for a flip kit. (can't recall the exact #'s right off hand) I know for a fact I'll have to change my headers (to those G body ones for $209) But other than that, and C-notching my frame...I think 5/7 will have to be put on soon