I was wondering what size jets I should run on my elco. I have a 350 4 bolt main block bored 0.60 over, World S\R torquer heads, Weiand Stealth manifold, Headers with true dual exhaust and cats, Comp cams 268 grind cam, Accel HEI with 50,000 volt coil and a 600 cfm Holley that has a dual feed fuel line. I believe it has 68 front and 72 rear jets with a 6.5 hg powervalve. It always runs rich. I don't know if I keep blowing powervalves or if it's jetted too rich or what. Any suggestions?

You should really check the plugs to get an indication of fuel mixture. If you're blowing power valves, (backfiring through carb) you should check ignition timing.

try jet the frt to 66 or 65 jets and rear to 68 or 70 jets

YOU DIDN'T MENTION IF IT WAS BACKFIRING, BUT THATS ABOUT ALL THAT KILLS POWER VALVES.THE EASIEST WAY TO GET THE TIMING CLOSE IS HOLD IDLE ABOUT 1200-1500 RPM (USE FAST IDLE OR FRIEND).ADVANCE TIMING TILL RPM FALLS OFF,THEN MAKE SURE ENGINE WILL CRANK WHEN HOT.YOU MAY HAVE TO BACK OFF THE TIMING A FEW DEGREES.NOW FOR THE CARB-GET ON THE HOLLEY WEBSITE + FIND OUT WHAT SIZE JETS + POWER VALVE CAME STOCK.THIS IS A GREAT STARTING POINT.ALSO GET A POWER VALVE SAVER KIT (NOT A BLOCK-OFF) + PUT THAT IN WHILE ITS APART.NOW CLEAN YOUR PLUGS OR REPLACE THEM + IT SHOULD FIRE UP + RUN FINE.I HAVENT ADRESSED THE DISTRIBUTOR OR WIRES,BUT MALLORY PROFORM + MANY OTHERS CAN SUPPLY THAT FOR $150-$225.
HOPE THIS HELPS !

I finally figured it out. 66's front and rear and a 8.5 powervalve. I also found out that for the last ten years or so Holleys have powervalve blowout protection. It still has a little dead spot in it maybe I'll try 68's. At least my eyes stopped watering.