how to align void cut in project file ?

[wfrst2008]

I have created a trapezoid void cut on the top of a beam
family and hope that when it is imported into a project,
one of the sides can be freely align to different ref. planes.
Two methods I have tried, by angle and by dimensional
constraints, but only the one by dimensional control enables
handles for freely adjustment, however, cannot use align tool.
Is there any workable ways to do that ?

thanks
Fung