The LokSound 5 nano isn't available yet. Maybe in July, maybe not. If you want to do the install now, use a LokSound 5 DCC micro. It should fit - maybe without much milling over the motor area, but if not, maybe in front of the motor area, milling off the "fingers" for the old PC board and a little of the chassis for depth.
Mill the rear for an 8x12mm speaker; I'd use a Soberton in a custom enclosure, but you could also get an enclosure/speaker combo from Streamlined Backshops (SBS4dcc.com).
John C.