Bachmann has made a couple of different GP40 models and some have the DCC quick plug and others don't. The first release of this model was a split frame DC only that didnt leave much room for a decoder. I installed an n scale decoder and it and it works fine. They later released the GP40 in the Spectrum line with no DCC quick plug but you could get a decoder that replaced the circuit board on the top of the frame. This particular loco isn't split frame and they upgraded the circuit board on the top of the newer models and have a DCC quick plug. Converting most engines to DCC is pretty simple with or with out the DCC quick plug. Hard wiring is not as difficult as it may seem to be, just do one and you'll find out how simple it is, if you follow the instructions that come with decoders that need hardwiring. Split frame engines take a little more thought and planning since a lot of the design of the engine's are really simply grounded contact points built into the engine that need's to be isolated from the motor. I've converted 3 loco's with split frames, it does take a bit longer, but it can be done.
hope this helps, Jim