INSPECTION: After a thorough cleaning most likely you will see minor numerous scratches and gouges in the housing's soft surface. Unless deeply gouged, most of these wear marks or machining imperfections can be satisfactorily smoothed over and polished to a glass like slippery surface.
SMOOTHENING: First take a 4" length of 80 or 100 grit emery cloth and begin evenly sanding the surface. Do not concentrate too much in one particular spot so as to not create any slight deformations, but rather evenly sand the entire perimeter. The goal here is to smooth out the scratches and grooves, not necessarily remove them. Removing them would create additional clearance between the outer rotor and the housing and therefore leaving in the grooves but just making them smoother would provide better overall results. Once the outer perimeter is satisfactorily sanded, move to the floor of the housing and do the same thing.
Once you have the entire inner housing sanded move up to 240 grit emery cloth and cover the same areas, thus smoothening the surfaces you just prepped. The 80 grit removed some minute material while the 240 removes the scratches left by the 80 grit. One that is completed, you can use a finer grit paper with a dab of oil to make the surface smoother and smoother before the final buff.
Once you have completed the sanding procedure your housing should look like the illustration to the right. Notice that the original deeper grooves still remain in the housing but are much smoother while the minor scratches are gone. This illustrates you did not remove too much material but you dramatically smoothened out what was there. Also be sure to deburr the sharp edges of the pump to reduce stress risers and eliminate these edges to chip off under operation and be sent into your oil supply.
POLISHING: During the buffing stage, use a hard felt buffing fob chucked in a high speed drill press or in a Dremel tool to polish the housing surfaces. First use Tripoli rouge compound for a coarser smoothening, then use the softer White rouge for the final buff to a high lustre. Remember to buff all the surfaces evenly & uniformly. Buffing compound can remove additional metal as did the sanding operating, so care must be taken not to use too much pressure or spend too much time during this process.
Finally, with a felt bit buff the inside of the hole where the inner rotor shaft inserts as well as the bore of the relief valve for smooth, slippery surface. Polish the valve too.
FINISHED PRODUCT: The illustrations to the right show the high lustre and incredible amount of smoothness that is able to be achieved. While the deeper grooves still remain, on purpose, the smooth surface will reduce friction and heat, and reduce stress on the distributor gear as a result.
As a side note, while the rotor-to-housing wall clearance can't be adjusted, the floor clearance can later on, so feel free to remove more scratches at the bottom rather than on the sides of the housing to increase flow and pressures. Be sure to perform this evenly and uniformly.
The photo to the right clearly shows how much more the housing floor is polished compared to the housing wall. The grooves in the wall will not notably affect the pressure or flow capacity, and in fact, the slight grooves will hold oil in suspension to provide an oil film for the rotor to ride on. The smoother floor will prevent oil seepage past the rotors when the oil is in the pressurization stage of the pump's rotation, and therefore increase pressure and flow as a result.