typically most bolt on stangs, ie pulleys, exhaust, TB, rockers, MAM, etc dont make more than 230 rwhp -/+ 10. The majority of H/C/I 302's make from between 280-320 rwhp depending on the combo.
I know someone with a stock 302 shortblock, box stock TFS TW heads, 1.6 RRs, RPM intake, FPS cam, 70mm TB, C&L mam, pulleys, LTs, H pipe, catback doing 311 rwhp. Thats with no ac, ps, or smog.
You can always make more power if your willing to spend more $$$ or sacrifice driveability.