Aftermarket 4" round speakers fit perfectly. Just make sure the tweeter horn (if equipped) does protrude beyond the speaker edge.
To get at the speakers, all you simply have to do is pry up the metal top panel with a screwdriver and pull it off. The speakers are one-wire. Any speakers you buy today will be two wire. Just run a wire from the neg. terminal on the speaker to a ground. By the way, forum rules say you have to post pics of your car or no more free advice.