Hi There,
Base model no frills cars came with the single dash speaker only but there should be mounting holes for 6"x 9" speakers already made into the steel plate under the rear package tray, if you were to climb into the trunk so you can get your head back up in there you'll be able to see them, at least that's how my 79, 79 (rip) and 81 two doors are/were, I believe four doors are set up for 4"x 6" speakers as the package tray is narrower, working from underneath you can carefully drill the speaker bolt holes and then several more holes around the speaker "oval" then from the top (in the back seat) very carefully cut the balance out with a utility knife or some sort of other implement of destruction and then you can put some good speakers in, that will save you from pulling the back seat etc, if you had a mind to you can put 4" round speakers in the lower door panel and as a matter of fact Dixie Restoration Depot has lower door panels to do such but they are a bit pricey, I personally don't care for speakers there but that's just my opinion, as far as the dash speaker goes I don't think you can get to it with out pulling the dash out of the car as I believe it's pretty much blocked by the defroster ducts, I don't have any experience with them but have seen some pretty interesting looking dual/stereo speakers made to go in place of the single dash speaker so it might be worth the work, of course I've done it several times but a dash can be removed from one of those cars in about a half an hour or so with the right tools once you pull the instrument cluster and find all the fastening points, they also made stereo speaker dashes that put one 4" round on each side of the car if you cared to hunt one down as it will go right in place of the single speaker dash, I guess that's all I've got, hope it helps!!! Later, KillerDave