6 x 9 in a 6 1/2

[Accord Man]

enclosure, as in box? (cause thats what it means)

But you probably mean the cutout.. In which case, there should be a template that came with your 6*9, place on the desired surface and cut snuggly around it.

You can use spacers and stuff, but thats a lame-O
way of doing it.