The loco will accept a "drop-in" decoder, which means it already has an NMRA 8-pin plug. So there is no need to modify one to work. The only thing that may need modification is the engine in order to accomodate the speaker.
You might look at the documentation for this one, for example: MRC - DCC Series - N GAUGE DIESEL SOUND DECODER, Item: 0001636, TRAIN CONTROLS/DCC
Andrew
You might look at the documentation for this one, for example: MRC - DCC Series - N GAUGE DIESEL SOUND DECODER, Item: 0001636, TRAIN CONTROLS/DCC
Andrew