Do you still have the early master cylinder?
If so, then Hooker made the only headers you can use.
If not, you may need to have custom headers made if you can't get them out of a catalog.
These headers are big enough, and will get you into the tens, but you have to run the original single reservoir mastser...which I do. I can remove the headers in less than 15 minutes, and change spark plugs blindfolded. You can run the heating system, but the wiring down the drivers inner fender is a trick. Unfortunately these headers are vintage units, and and no longer made. They will require some searching.
Forgot to mention the car was an original D/S, then D/MP car.