Looks like your best bet might be to remove the metal cage holders and cut off the indentations for the heater controls , when you put it back together put the heater controls at the bottom and the empeg in the center so that the heater controls give it some support and also the vent on the top of the empeg won't be convered by them.

The metal frame is used for the earth on my 200sx/silvia (for my other head ,not the empeg) so it all might only work once it is back together.

I assume that this is the same as your interior?

you might also want to ask the same question on stereo mounting on the UK skyline board www.gtr.co.uk

C.