I saw a chopper at Windber with a Polaris twin cylinder it was painted and done up to a show quality finish. it was a beautiful bike. but unfortunately I never got to see it run. so yes it has been done. there are also dome drag bikes on youtube with snowmobile engines. the hardest part of the build would be finding a good spot to fit those huge expansion chambers. a build that's all about power like this isn't worth doing without them because you would loose to much power.