As pumps go, that one looks pretty good. I have almost convinced myself it is a cast iron body, (or maybe just a trick of the light) and the score is in the scavenge (larger) chamber. The wear marks on the end plate are relatively minor, but more importantly the sharp edges of the chamber appear undamaged, which is good. If it was mine, I would use it without question. If you are not inclined to retain it, use it as a trade in with one of the established suppliers of new or recon pumps.
Check all the gears have the same tooth profile. Several different types were used, they may have been mixed and matched in an earlier life.
As mentioned, the gears like to be returned to their original positions if possible, but in all honesty I do not know anyone who actually ever achieved this. So the trick is to start with one gear, then add its chamber partner, moving this gear tooth by tooth to achieve the most free rotation.
Once happy with this, and all gears freely rotating, add the spindle housing and end plate, but tighten gently, also twisting the three parts, spindle housing, body and plate as the bolts are tightened, turning the drive spindle all the time, making sure free rotation is maintained as the parts settle and are finally tightened. Sometimes the gears will turn easily but lock up when the drive spindle is added, this can usually be fixed by refitting the spindle but rotated by half a turn. There is more information elsewhere on the Forum
Remember this forum is world wide, and you may want to consider another way of posting your pictures.
Swarfy.