I did it on a 1978, using a Dansk repop tank. It was tight, but doable. I used a banjo bolt fitting for the return to the smaller center tank fitting, used the factory screen outlet in one of the larger fittings, and plugged the third one.
This is the best pic I can find from the BaT auction listing:
https://bringatrailer.com/listing/1978-porsche-911sc-60/
There may also be more pics and details in the build thread:
https://forums.pelicanparts.com/porsche-911-technical-forum/979976-project-heavy-metal-all-steel-classic-remastered.html
One thing to note though is the early tank does not have a swirl pot. Not an issue with MFI (which I ran) because the filter console in the engine compartment de-aerates the fuel before it's delivered to the MFI pump.
The fuel pump in the pics is a 3.2 Carrera pump which had conveniently sized fittings for what I was trying to do.
Hope that helps!