Aerial wire routing

My Mk2 has a dead radio installed which is not connected to power, to the non existing speakers or to the roof mounted aerial.
I install a new radion (which looks sort of OK) rigged up 2 3" speakers behind the speaker mesh however I can’t figure out how to route the aerial wire from the centre roof aerial down to the radio.
I removed all the timber trim which allowed me to feed a concealed wire from the centre to the top left corner of the windscreen but from there I cannot find a way to
feed this wire down to the space behind the dash.
There must be an obvious way but I can’t see it. All help would be greatly appreciated. Ron

I don’t have roof antenna, so no experience, but if this photo tells the truth, there is a hole in A-pillar top, through which you might get a wire inside A-pillar and hopefully also out somewhere at the bottom of A-pillar/fender wall?