Here's a few pictures that might help.
Unrestored speaker bracket. Note the insulating foam. That side goes against the dash to prevent speaker rattles. Not my picture, but I had it saved.
This is my bracket after stripping, painting, and adding new insulating foam. The foam is just home store self-adhesive weatherstrip. The speaker is covered with acoustic fabric and attached to the frame, ready to be installed.
Backside of the speaker. This speaker, Retrosound R-410N, has two tweeters that can be wired for stereo, giving a 4-ohm signature. When wired for mono as pictured, it gives an 8-ohm signature. The instructions on how to wire it are on their website, I think. If you can't find them, message me with your email address, and I'll send the instructions to you as a pdf.
This speaker sounds OK with a stock radio. If that's all you're looking for, you'll be satisfied. When I drive my car, I want the retro experience for nostalgia, lousy radio, wind noise and all. Brake, tire and suspension upgrades are the exception.
This is someone else's picture of the dash inverted. You can see how the bracket attaches to bolts whose heads are covered by the defogger outlets. The bolts are flat headed carriage bolts with square shanks, that fit in a keyhole shaped opening. The keyhole is designed so the head of the bolt can be installed from under the dash, then slid to the narrow part of the opening. Once there, the square shanks allow you to tighten the nuts holding up the bracket without spinning. If you don't have your original bolts, you may need to modify some that you source locally. I went to a few places before I found bolts whose shank was the same size as the slot in the keyhole opening. That was about 1/4", but I don't recall the exact size. Then I ground the rounded head flat to fit under the vent outlets without interference. If you remove the outlets, this will all become clear to you. If you do, be careful of the plastic studs on the outlets. They probably have a limited number of times they can be removed and won't respond well to rough treatment. Repops are expensive.