performance upgrade ?

the only way to know for sure is to dyno it. Some times "some" perfomance parts really dont add to the Horsepower but instead it helps it. Although if I was to make a guess, I would say you are in the 255-275 horsepower range. If you add a "cold air" with a "K&N - like fliter"and put 2.5" dual exhaust with "good" mufflers, and a under-drive pulley set up, you can go over the 300 mark easy.

I had a 86, The 305 was hurting when I bought it, I put a 383 "stroker" in it (a 350--> bored and a "400" crank) Aluim heads, FluidAmpr balancer, underdrive pulley's, 750CFM q-jet plus a whole lot of other stuff, But I dyno'd in at 377 to the rear wheels. The onlt thing I had to do was get a truck tranny and a custom/balanced driveshaft. Lots of memories....... Have any pics??

not much ! the most you can get out of a 305 is about 300hp. it all about cubes. could have bought a 350 for much less.