The following might be helpful:
Drivers - 8mm (confirmed)
Housing width - 10mm (measured from the inside edges) opening, tapers down to ~5mm
Housing depth - ~12-13mm (I don't have anything small enough to get inside for a more accurate measurement)
I don't know much about modding, but IMHO these look like they would be great for it.
Just a word of warning....take care removing the drivers, if you want to keep them. They are glued in with a foam band. I destroyed both taking them out :( Oh well...I've got two back up pairs anyways.