Rebuilding the engine and replaced the stock distributor with an HEI. I'm struggling to find spark plug wires of the correct length. Any help on a source? I already tried JEGS, NAPA, and AutoZone. Pic below. Thank you.

 

I tried a shot in the dark, ordered TWO sets (different brands) from RockAuto for a 400; one set fit perfectly. I can't remember the name... The "OEM" brand didn't fit.
I got separators off a junkyard 400 for the 8mm wires and they were an exact fit for the FE valve covers.
Eric

 

I bought a set of Taylor wires that were cut to fit. I believe that the dizzy connections were already made, and I just had to cut and fit the spark plugs. If you get wires larger than 7mm, they won't fit the holder at the valve cover.

 

Have a set of Ford Performance 9mm on the 65 w/ 302, and currently installed a set of Taylor on the 65 w/ the 390. Both w/ 135 degree boots and made to fit. Really do not have an issue with Taylor, I tend to prefer the Ford Performance, Summit offers the same Ford Performance kit for the 5.0 and 5.8 come in different flavors. When/if I were to replace the Taylor 390 wires I may try going with Ford performance and possibly the kit for the 460, believe same firing order, according to Summit the 460 wires slightly longer? Family now affectionately refers to the black truck as ole 'Smokey'. Now in process of using harness wrap on the exposed wires.

 

The 8mm wires that fit for me are "Armor-Shield" brand for a 400 (I opened the hood and had a look!). When I said they fit perfectly I might have exaggerated a little - they are slightly long for a '66 352 but they look right and are long enough to work with tall Mercury-script valve covers, whereas the originals were not.

 

+1. Requires you route them around the VC's instead of over them which I prefer, and the have 75° (?) boots that clear the manifolds nicely.

 

Mine went in the stock location which the looms from the 400 allowed.
Eric