Gears will make the car feel faster though it won't actually be. Cams can give a decent gain up top on PI-headed engines but the gains are coming at the top of the rev register. My personal opinion is that most bolt-ons are not worth it; the cylinder heads, small bores and generally tiny displacement (281 cubes...) work against seeing worthwhile gains with stuff like throttle bodies and plenums.
I'd avoid underdrive pulleys, full-stop. There was some evidence from years ago that the poor damping characteristics of some UDP cracnk pulleys could lead to oil pump failure. Simply not worth the 1-2HP you might see from them
Save for a blower. Make 281ci feel more like a good 351 for a few grand. The stock bottom end can take enough boost to make 400rwHP with reasonable safety. Also, think about suspension, chassis, brake and tire upgrades to make the thing handle and stop.