Owned a 84 z-28 crossfire, ugly system all talk, no play. That plenum sitting that long, My guess is you have a huge vacuum leak. As its a plenum many dont think its 2 pieces.. and just check around base and injector areas. I find leaks with some starting fluid (be very careful, to much and its not good) when cranking spray around base of intake (NOT INTO IT!!!) see if it fires, you have a vacuum leak. Have seen the plenum gasket bad on many of them. Of course you are saying an injector isn't fireing, swap um around, see if its the injector or elsewhere.

mine had a shorted tach wire that cause all sorts of problems starting (not like your problems) but wouldn't hurt to unhook the tack from the distributor to eliminate one other trouble spot (brown wire if I remember right).

one thing, with that old of car sitting, gas? it takes along time to move through all the lines and get fresh if you didn't drain it.. grab a small oil squirt can put some fresh gas in it and squirt a few shots in each injector area, fire it up and see if runs for 1-3 seconds..
how many miles, small block chevys don't have much timing chain problems unless they have excessive miles. They have been know to break a camshaft (unlikely) pop the cap off the distributor and crank it, make sure its turning. Broke cam and it will sorta turn on and off.

that is of course if you have treid the other great suggestion here (wires!)

good luck let us know if you figure it out.