After doing a lot of internet searching techinspector1 was right on the money as far as the heads go. They're not as bad as 305 and some 307 heads, but they're nothing to write home about. A good set of vortec's or aftermarket aluminum would be your best bet depending of what kind of power you have in mind.
You can run 91 octane in that engine but all you're doing is throwing money down the toilet. It'll run just as well on 87, but it's your vehicle and your money.