> Is any of this code necessary on a 64 bit run-time?

AFAIK, there is nothing special with 64 bit. If you sure every struct on platform *X* is properly *n*-bytes aligned and the class requires *m*-bytes alignment where *m* <= *n*, you just tell compiler that `Scoped` struct is *m*-bytes aligned (not sure about the proper way to do it, maybe `U[0]` will help but note about [Issue 5332](http://d.puremagic.com/issues/show_bug.cgi?id=5332)) and branch out alignment code.