I don't know what an IM is and my expertise is limited to installing two transponders by following simple instructions.
Installation of a Funkwerk TRT800, which comes with the cable assembly, requires a crimper, a screwdriver, a heat gun for the heatshrink and a Stanley knife for the Tygon tubing. For the aerial you need the knife, heat gun, a couple of spanners and a drill.
The LAA inspector signs off the work, it is tested with ATC, as mentioned earlier, and the paperwork is sent in for approval. With that in hand, I am free to take to the skies and become a menace to all those pilots who have to pay a fortune to have their equipment installed by professionals.