Make sure that the wires won’t touch the exhaust manifolds, get caught in stuff like the fan belt, or get cut on sharp edges. Check that wires firing sequential cylinders (like 5 and 7 on most V-8s) cross at right angles (if possible) to prevent crossfire. Cosmetics are a big issue with plug wires--avoid big loops and use separators to keep them neat. Don’t make the wires so tight that you can’t remove the cap or rotate the distributor for timing adjustments. Once length is determined, cut one wire at a time then double-check the fit. If you cut it too short the first time you’ll be out of luck unless it will fit another cylinder.