12.8 to 13 in good.
12.8 is conservative, 13-1 is still safe but might get a little
more HP. at 260hp level the diff. is minimal.
a good tuner will try both and set it based on the best results.
Looks a little lean though, like said. I made 248.9/285.9 with Dr gas O/R X, magnaflow CB, P&Pd TF plenum, custom sealed ramair with K&N (doesnt help on the dyno, it hurts), electric water pump, SCT-4 back, and 3.73s. Yours and my gears will rob around 5RWHP on the dyno BTW. My A/F was all over the place but was mainly between 13.9 and 14.9 LOL. You need a tune, with that you should hit a good 260-265 easy.