if you have the cage, then you mount the cage first. Mount the dash kit first in the dash. Then slide the cage into the hole. Make sure it sits all the way back and is flush against the kit. Then use a flat bladed screwdriver to bend the tabs on the cage out so that the tabs wedge the cage against the kit. Do a few on each edge so that the cage is very strudy.

Then add your wiring and slide the CD player into the cage and voila! You are done.

www.installdr.com may have some useful tips for you.