Hello
Yes it is somehow a direct bolt on. You will have to drill some holes for your window mechanismen but you will find those places marked with a little recess for direct drilling.
You also will find retangular holes for the plastic rivets used in 78 on doors ( pre 78 are boltet direkt to the inner skin or have the little sliderplates with the dual threats on the lower edge ).
While you are there reinforce the rear door pcket flap anchor with a secound sheet from the rear ( I have them as ready threated units and just use a rivet in the middle ).
Now a other problem is that the door will not have the same curve on the lower a-pillar and not press the interiour light switch deep enough. You need to glue a piece of rubber onto the door ( see 356
) or shim the lightswitch.
There was a rumor that Porsche will sale longer switches to solve that problem "cleaner" but never heard from that the last 10 years again.
Grüsse