I have a 351w enging that is missing on cyl 1,6 and 7. Have changed complete ignition system, carb, valley pan gasket twice, had intake manifold checked at machine shop, good compression and everything else. I am stumped, does anyone have and ideas?

 

Missing when cold, warm hot?

If hot, are plugs the correct heat range as different cylinders run at different temperatures?

What year engine?

Definitally replaced cap, rotor, plugs, wires, capacitor and so on if applicable?

Checked all vacuum lines for leaks?

Tried moving the 3 sets of plugs and wires to 3 different cylinders to see if problem moved or stays put?

 

Engine misses when hot or cold, have changed plugs, wires, new electronic distributor, I did change the firing order, their are 2 different ones and got #6 cylinder to hit. #6 is the same on both firing orders, but #1 & #7 still dont hit. Had the heads reworked , manifold checked, carb rebuilt just am dumbfounded.