I know this really doesnt help since i've got a 7M, but I took the plenum off first before removing the rail + injectors. It was coming off anyway (blown gasket fix, ahh 7M's are wonderful ) but removing the plenum will make it easier to access your cold start injector and give you more room, so reinstalling would be much easier. Dunno how the 5M's are set up tho.. cant you tell by looking at how much room you've got between the rail and intake??