Show us pics of the dash and door cards; you can fit small 3" speakers in the grilles above the outer vents on the MK1 westy dash. If you have door cars that have built-in map pockets with speaker trays, then just measure the old speakers and replace with ones of comparable size. See about upgrading the speaker wires at the same time since the old ones are 2-3 decades old. You could also put the speakers under the seats, but that involves fabricating mounting boxes. AS far as the head unit, just pick one with bluetooth compatibility and you should be good to go; it's hard to find an inadequate head unit these days.