to install in your head liner what I would do is.
1. get measurements of the radio, and make up a template out of cardboard and stick it up to the headliner to see how it would look.
2. You got a couple of choices on how to make your pod, you can make something out of some cabinet quality plywood, HDF(high density fiberboard), or some cheaper wood and cover it in body filler to get the shape you want, then coat it in some fiberglass mold release, cover in fiber glass let it set and remove now you have a mold for your pod. coat it again with mold release, place your fiberglass inside your mold w/ your bracketry to hold the radio in the pod, let it set and remove paint or cover in your choice of carpet, vinyl.
3 cut your head liner to the opening to what you need, after you've removed it to see what you have to work with. you can then attach your pod to your headliner w/ staples, and cleats of wood to attach it.