DOCDRS,
There are several issues with those particular Roswell pods.
First, the plastic interior mounting ring needs to have the I.D. enlarged.
Second, the ring is held in place with a 'V' shaped strap that extends to and is mounted to the nose of the pod. A deep horn and rear-mounted crossover is likely to interfere with the tapered bracket.
Also, this mounting arrangement isn't really designed to facilitate anything more substantial than standard coaxials.
I would either replace the existing interior mounting rings with new HDPE ones that use set screws around the perimeter of the pods for mounting
or
I would glue and seal in place a couple of 1/8-inch thick aluminum rings at the interior face of the pods.
In either case I would have a stable foundation for my new HLCDs and do away with the light duty bracketry inside.

David
Earmark Marine