For those of you that have 'modified' your rear speaker mounting brackets, here is the price quote I received from St.Charles...

Quote from email received from St.Charles Isuzu
The rear speaker mounting brackets are 8-97176-236-4, and
8-97176-234-4; list price of $110.27 each, your cost $93.73.
Looks like I may try and fabricate my own somehow.