A larger master cylinder will indeed make your pedal harder , but will also decrease the travel of it .
Have a look at the 997 gt3 one ... 997 355 910 30
Try searching on rennlist for posts by bill verberg , he ALLWAYS used to post all kinds of info on interchangeable brake components and gear ratios etc.
I'd look for you , but I have been banned many years
Maybe Have a word with porterfield etc as pads will also make a difference .