Title sez it all; Spent the last two days doing it the old-fashion way. I will touch on the things others could use.
1) The exhaust manifold heat shields are a little tough. In both cases (left/right), if you can remove the O2 sensors this will help significantly. Remove the heat shields which protect the engine mounts before fighting with the main manifold heat shields
2) Note that there is a left and right O2 sensor lead extension for the rears, they are keyed differently.
4) Watch the clearance on the rear O2 sensors, with the Kooks system you can rotate the CAT pipes such that they can be positioned away from the body underside. Make sure to center the pipes to ensure adequate left/right clearance as well, there is little room here for error. The amount of compliance in the engine and trannie mounts will allow alot of side play during spirited driving, which pushes the tops of the O2 sensors close to the body! if you stick a 13/16" long socket on top of the cross brace, between it and the crossover pipe, once you have everything tightened down and remove it...that crossover pipe will rest ~1/5" above(!) the top of the brace. Plenty of room to bounce without hitting the brace. Some people remove that brace permanently, this is not a wise idea given the significant role it performs during a significant impact.
This shot is looking across to the left/rear sensor:
This shot is looking straight up at the right unit, What you see is the felt insulation, and slightly to the right is the belly pan/driveshaft tunnel. Not a lot of room.
This shows the heat shield protecting the brake lines that head to the rear along the right hand side. Note the coupler rings have been offset (rotated slightly) to avoid contact. It's tight here as well:
Finally, the Magnum was raised only this high:
Sliding both headers in and out was a breeze, I did it a lot to fine-tuning for fitment. In fact I mounted both the header and the Hi-flow CAT's simultaneously so as not to have to shift/drop the rest of the exhaust system. Worked like a charm.
I did not have to remove the starter, nor the fusebox assembly up under the hood with these Kooks headers. It is imperative to disconnect the negative lead from the battery, as a quick check with a DVM revealed 12V on that big bolt sitting on top of the starter housing...just waiting for an errant wrench/heat shield/header/etc.
Finally I used the supplied hardware. I thought about all the times I have installed headers and the number of times any bolts "actually" came loose. Near as I can figure that twelve sets...maybe once. I did reuse the OEM stainless steel gaskets upon the advice of Kooks. They admit the gaskets they supply are, well, satisfactory as coasters.
The exhaust note has changed significantly. It has gone even higher in frequency, and is now downright aggressive under load. My neighbor was keeping an eye on me just in case Maggie decided to try and compress my arse while working underneath her, he came out after I came back from a spin to say it now sounds like a Rousch Stage 3 Mustang. "Vicious and Crackly" were words he employed. This sound clip sucks, I'll get another "going away" clip (like in my sig) when I get a moment: