Did a little research, searching on the internet for routing plug wires turned up no useable results. Read some documents from MSD, Plug Wire manufacturers, and trouble shooting ignition problems related to wire routing,.... Drew about 6 versions of the routing diagram before I found one that worked well. OK, I know, how boring and way over thinking it. The fact that I couldn't find one mde me think this must be a trade or car show secret. So to save everyone else the boredum, I'm sharing my results for routing plug wires off the back of a small block chevy and under the headers so that it looks good, simple, and avoids issues at high and low rpms.

Routing guidance from MSD: Correct routing of the plug wires is also important to performance. Wires should be routed away from sharp edges and engine heat sources. If there are two wires that are next to each other in the engine's firing order, the wires should be routed away from each other to avoid inducing a spark into the other wire. For example, in a Chevy V8, the firing order is 1-8-4-3-6-5-7-2. The #5 and #7 cylinders are next to each other in the engine and in the firing order. If the voltage from the #5 wire is induced into #7 detonation could occur and cause engine damage. (from MSD’s instructions)

Since you can position the #1 on the distributor cap anywhere, I decided to make as many Odd #'d distributor contacts/wires start on the same side of the block as the Odd #'s cylinders. Works out pretty good -- 6 out of 8 wires don't need to cross over or around the cap, plus the 2 wires that do need to cross over actually help to avoid the situation described by MSD of 2 adjacent wires running together.