Need new plug wires on my Elky so went out and bought a set with the ends that fit onto the HEI. Was reading the box and it says that they are 8mm. I have a set of new wires in my shop that are 8.5mm but they don't have that special plug end that goes on the HEI cap. Will they work anyway? Are those ends the only difference between HEI and regular plug wires?
Thanks!

Yes, but they are a little bit of hassle to crimp on the right boots.

Bump

Most likely the difference, other than the ends, is the thickness of the insulation. With resistor plugs and the air gap between the spark plug electrodes that the spark has to jump across you end up with quite a bit of resistance. With a super hot coil, very high voltage output, that voltage might decide to find a different path to ground. What can happen when the plug wires are tight up against each other or touching part of the engine the voltage can punch a hole through the insulation. You'll get crossfire between 2 wires or short one cylinder to ground.

Thicker wires just reduce the likely hood of this happening. Either set will work and unless you have a really hot coil probably won't make much difference.