The cam you're running now is out on the ragged edge of being too big for the 7.8:1 static compression ratio. 69elko is right on the money with the 0.8 compression ratio change when going to 64 cc heads. 7.81 to 8.69. Use the 12558060 L31 Vortecs if you want the best low-buck iron heads. They'll flow better than any other OEM Chevy head and probably better than most of the aftermarket iron heads. They're perfect for a 350 with flat-tops. You'll have to change the intake to a Vortec-specific manifold, use rail rockers and center-bolt valve covers. Keep the cam you have now. It's perfect for a 8.69 c.r. and your 0.453" valve lift should clear the stock valve seals.
Here's some blah-blah about the L31's....
Scroll halfway down and click on "GM L31 Vortec Heads"
http://www.gilbertchevy.com/frame.ht...ankshafts.html