Are the black pieces that hold the wires plastic or machined aluminum?

• Does it matter if the spark plug boot is straight or 90 degree? Is it the same for stock exhaust manifolds vs. headers? availability
• They don’t appear to be adjustable. Do you have a measurement between the two mounting holes? install
• Do you make these for sbc i have a 67 c10 with a sbc. I like these looms but the one's you are showing are Ford's thanks general