03 Olds Alero Head Unit Too Long

I have been trying to install a Panasonic head unit, I think it is 5403q or something close to that, but when I go to put it in the factory spot, it is too long.  I compared the unit to the stock radio, and it is longer.

I have the kit that makes this unit fit in the factory spot, and will fit the holes, but will not push in far enough.

What can I do to make this unit fit in the car better?  I have thought about either cutting the plastic from the back but this is very hard to get in and do and there is some metal back there too which would also damage the factory radio mount if that ever was to be installed again.  I have also thought about getting the faceplate that puts the radio further out in mounting, but am worried this might make it look funny.  Also, if the trim ring is on the radio, it will not fit very well in the rounded corners of the trim panel that holds the heater controls and such.

Thanks for your help, my friend is leaving in two days 600 miles away and I need to get this done for him before he leaves!

Thanks for the reply, I have been busy and did not reply lately, but did take your advice, I told him we were going to cut it, and before we could get going, he informed me that he had taken it to the local stereo shop and had them finish it for him because he couldn't wait an extra half a day.  Kids these days...

Thanks anyway for the response and next time I find something like this, I will know what to do.