Was thinking about doing the exact same mod, but don't have any spares lying around and I don't feel like taking my e-revo or muggy apart right now. I do have a revo and muggy diff case and measured the dimensions of both. Differences in lenght, width or height is no more than 2mm.

Revo outer diff case width / length / height: 35mm / 54mm / 43.3mm
Muggy outer diff case width/ length / height: 37mm / 55.5mm / 43mm

So, subscribed to this thread to see your progress. For it to be a cheap mod it would require to keep the stock front, rear and center driveshafts. Centers are probably covered with Mike's couplers. But how about front and rear driveshafts?