Hi MAZDA6MPS, The CP_e DP install instructions are basically fine. Definitely be prepared to undo top right and bottom engine mounts and drop the engine forward. Be careful when you lean it right forward to avoid damage to the radiator assembly and fans. Keep the jacks in place so you can move the engine about as you tweeze the DP and its shields out. Remove all the manifold heat shields and clutch master cylinder heat shield. Remove the cat O2 sensors entirely, from the plug ends under the battery box and turbo inlet pipe - it saves twisting up and breaking a lead, which is still possible even when using an O2 sensor socket. Keep them somewhere safe. Be patient lubricating them and unscrewing them, in and out a little at a time until they unscrew freely.
I found even then it was tricky to get the stock DP out without scratching the firewall until I undid all the nuts holding on the heat shrouds, and carefully peeled them off the DP one at a time - it is a @*%$! bitch due to odd shapes and studs and mounts sticking out. Remove the old DP mount bracket (gold coloured) or you will get hung up on it forever as you try to get all the old bits out. You need to access it from underneath, largely by feel. Make sure you have a torch throughout all of this process anyway. Some of the shields you have to drop out through the limited space at the bottom. Then it is easier to get out but you still have to hold your mouth right.
The old DP comes out the top - gently and slowly and by carefully rotating as required to ease it out and avoid scratching the firewall and messing up the fixed foil insulation there. The new DP goes in easily, from top or bottom, depending on how high the car is off the ground. The inner studs are tricky to torque up but it is achievable. You may have to access the stud nuts from below with a long wrench. You can re-use the turbo gasket if you don't mess it up getting the old DP out.
I found a 3/8" drive socket set better through the whole job as the drive extensions take up less room than 1/2". Get extra extensions of a variety of lengths. It saves some teeth grinding.
Good luck! :-)
CP_e Standback & PNP; CP_e 3" SS Downpipe; Corksport FMIC with Top-mount K&N filter & OEM Ram CAI; Turbosmart BOV; Dashhawk; Prosport Boost Guage; JBR solid shift bushes; DBA 4000 Wiper-Slot front rotors; Hawk Ferro-Carbon HPS Street front brake pads (@ 69,000km); Sumitomo HTRZIII's in 225/45 x 18