simple, cheapish solution would be to get a set of new full range (2 or 3 way) speakers for the door pocket position and give up on the dash top ones.
a bit more money, a set of components, that would come with the required crossovers. the mid would go in the doors and then the tweeters could be fitted either:
further up the door card
into the backs of the wing mirror plastic trim (like mine)
or into the dash top position
not too tricky hopefully
