Honestly, 3" pipes are not a good idea for a puny (sorry, but it is) 305. 1 1/2", maybe 1 5/8" headers with 2", 2 1/2" exhaust (per side, use a crossover point) are all you will need. I have the exact same engine my car right now, with a 350 sitting outside, and I'll only be using 2" exhausts at...