Judging by the length of the RetroSound shafts (tuner, volume etc.), they are not long enough to mount a speaker panel. Regardless, the RetroSound shafts are not strong enough and would probably break from the weight. You will have to make your own speaker brackets. On the left side is an dash brace going to the firewall. GM used this brace to attach a mounting bracket. On the right side, unfortunately, I have no idea.
One thing about a cowl vent. If open and rain happens, your radio and speaker can get wet. I would fabricate a shield of some kind for protection.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
