I have a spare HR lower manifold!
As far as I could see, there wasn't much to be taken off the ports, some slight casting marks, maybe a little more flow on the backside (as the castings for the plenum mounting screws protrude) and a perhaps some from the injector ports.
The problem I see though is taking too much material from the injector ports. If you do, the air may not flow correctly for the fuel injector spray pattern.
Also, if you don't match the cylinder head ports to the newly ported manifold, the flow will actually be worse.
Proceed with caution!