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If you have the factory 84 truck exhaust manifolds the plug wires on #1, 3 and 5 run under the exhaust outlet next to the block right past # 7 plug where they pick up #7 and the 4 (1,3,5,7) continue up behind the head to the dist.
Sounds crazy but you cant run them over the valve cover cuz of the exhaust. As you have found out.
Also the wires are all 90 degree boots except for one is straight. (#6 iirc)
If you get headers you don't have this problem.

If you have actual "ram horn" exhaust (we used to run corvette ram horns on our circle track car) then run #5,7 and #6,8 up the back side of the heads and #1,3 and #2,4 up the front side of the heads, across the top of the intake to dist. That's how we used to do it