Pretty slick. I can see an old Villiars midget (100cc) sitting in that cradle and giving the bike a nice old time look. For that matter the model 1932 Fitchel & Sachs 2 speed motorcycle engine(also at a hundred cc's) would be the cat's meow. I have one on my Hiawatha tri-car that was made in 1934. Your cradle lends itself to mounting any number of vintage motors I would think.
SB
SB