I have an 87 iroc its a green elephant. It has a 327 block 305/350 intake quadrajet carbon and 305 heads. The car starts and isles very smooth, put it in gear and it shakes. When driving under load it sounds like its missing, it shakes the entire car..any idea's

 

Sounds like it could be a vacuum leak. Start the car and spray some carb cleaner around all the vacuum hoses, intake gaskets, and carb base gasket. If the idle changes....you've found the leak. It might help to put the car in gear while you do this, of course you will need someone to hold the brakes for you.

If that checks out, I'd start with the basic tune up stuff. Filers, plugs, wires, timing.