OK, into it.
The 450D is now in bits and the IR Mod has been done. Gary Honis's instructions are invaluable especially now that others have offered extra tips. I butchered ... err modified the case in two places to get access to buried screws. A left side screw that holds an earthing strap and the top screw for the sensor assembly hidden behind the viewfinder. Pix marked with arrows for anyone who wants to think about doing the mod. I broke the IR glass (as Gary did). It is very thin and won't be used obviously. Just be careful to clean up as you go, dust, chips of glass, finger prints etc.
Biggest problem is it is full of connectors, heaps of them all over the place. There are connectors under connectors and some are quite short and are hidden up under the top case. Reassembly will have to be taken very carefully and I can see why the left side cold finger access method is about the only really viable option.