+1 for Otter74 suggestion. Buy the kit from Enhon bleeding kit from Amazon and bleed the MC.
For my '83 SC, I bled it on the bench. But, as Otter74 says, can be done installed in the car.
I went through this challenge about a year ago. Here's my thread for your reference:
https://forums.pelicanparts.com/porsche-911-technical-forum/1166024-help-bleeding-brakes-83-sc-new-master-cylinder.html