Hello sir.
When swapping the 87-89 trans cover to a later 90+, you will need the shorter shifter shaft. The tail cover lists from Porsche for about $1000, but I can get one for about $50-$100 cheaper to you. The shifter shaft can also be modified to fit the 87-89 box with some relatively simple machining, or I have a short shift shaft in stock For Sale.
Take care sir,