Newer "small cap" HEI's use 7MM wires, so the 8's would be fine, I'm sure. They also fit the terminals on big-diameter caps correctly. The large diameter cap and rotor was also designed to combat a mostly nonexistent concern about crossfiring that's been pretty much debunked. Now, if plug gaps get huge due to neglect, or a plug wire falls off, then the coil has enough open circuit voltage available to jump right through coil insulation, etc. As long as the voltage has somewhere normal to go, any size wire is probably OK.
Jerry
