I very much doubt it- the single speed 3908 tranny uses a 33t output gear, vs the 38t & 43t gears in the nitro tranny. Both have a 13t idler gear, which makes fitting a different sized output gear impossible.
The gears in the 3908 tranny are very strong though, haven't seen anyone strip those yet despite being made of plastic ( top gear and idler are steel, output is plastic ).