Hi
I used mirrors from an Australian 70s Ford Falcon just like the one Mel Gibson drove in Mad Max/ Road Warrior
on my bug. I cut the stock Ford mounting leg off, and glassed over the hole, then I got some stock Beetle mirrors, cut the mirror part off so that I was left with a stump, drilled and tapped it and bolted the Ford mirrors to the stumps, the mirrors use the stock VW mounting hole, no extra holes. Im sure you could do something similar with the Porsche mirrors.
My car with the Ford mirrors,
Steve C