The easiest way to replace the rear plugs and wires is to: 1. remove the front engine mounts (dogbones). 2. leave car in park and push forward until the engine just touches the fan. 3. depress parking brake. 4. remove the bar connecting the struts.
Its still tight back there but at least you can get a socket on the plugs.
I question the diagnosis of plugs, wires and injectors. My Regal just had the same problem and it was the catalytic converter.