need audio help/suggestions

[54chevytruck]

I recently got a 54 chevy c3100 that had a new audio system put in it in the late 80's it has 1 speaker in each door and 1 speaker behind each of the bucket seats. the head unit has a cassette player and might have a cd player but i dont think it does.(the truck is about 70 miles away from me for the next few weeks)

I was looking for suggestions to upgrade the sound system. I can deal with the old head unit for now, but i would like to put in better speakers. there is a compartment under the passenger seat, i was thinking about mounting an amp down there maybe? if so i have no idea what type.

Also, the gas tank was removed from behind the seat so there is some extra room. should i get an enclosed sub to put between the speakers back there?


attached is a picture of the truck and the interior. the square in the dash is where the head unit is(sorry i forgot to take a picture of it)

any comments would be appreciated

thanks,

Austin