I was thinking about doing a similar retro fit on my 75 but I will probably do 2X250 watt with 14k lights and use 2x65 actinic pc's. If you are handy at all it will be easy to install in canopy. Everything is pretty much pre wired you just have to mount your reflector and your moguls into the canopy which just takes a few screws and put your ballasts under the tank or somewere dry. the only thing is the 400w's will put out a lot of heat maybe consider the 250's which will be plenty on a 55 unless you are planning an upgrade later.