Had to go back through to see what the plans were for this engine. Ok, so WEEKEND TOY is what I found.
If you want a weekend toy, use your 781`s. Put 2.25/1.88 valves in them, do some bowl work, short turn, gasket match, shape the guide bosses, go to a 11/32 valve to help with the flow and be done. If your going to do the 489 then worry about building torque. Thats what puts you in the seat and thats what we all want in a street car. Plus it will be less finicky to drive around.
Once you get the heads done you can pick your cam. Make sure you get flow numbers because without them you may as well throw darts at the board for cam choice. I`m going to suggest Chris Straub again for the cam because he has a proven record when designing camshafts. Check out this site and look up Cstraub,
http://www.chevelles.com/forums/forumdisplay.php?f=13
A good cast steel crank from Eagle or Scat will be more than you need and is budget friendly. Stick with I-beam rods and I would suggest Scat rods with the capscrew option in either 3//8 or 716 in this case.
Pistons, you need a 18cc dome to get 10:1 with your heads which should be 119cc chambers. SRP or Probe would be good. You might find a Icon piston that works as well. You could even go with a smaller dome for slightly less compression. Bigger engines need less compression to make the power. Here is a good place for a quality, budget friendly rotating assembly,
http://www.coasthigh.com/Chevy-496-e...me-s/13123.htm
I understand what your trying to do. Get some "hi performance" heads at a low cost but the fact of the matter is sometimes the headaches these cheap heads create end up being more than some top end parts were to start with. Build a good solid shortblock now, heads and cam can be changed later on. There are so many guys running 496 engines with 78` heads with the little bit of work I suggested that are very close to the 600hp mark and the same in torque or more. Do some research before buying a bunch of parts. Everything needs to work together. I`m trying to help you the best I can but you know what they say, you can lead a horse to water....