If you are still trying to fix the end plate with stripped threads (if I understood the posts correctly) what you could do is get a peice of "01 GAUGE PLATE". And make a new one, in its unhardened state it is drill and tapable and will be gaurenteed flat to tool making specs. It comes in 12" long peices and isnt that expencive.
Its realy good material and as tuff as. You wont strip a thread in that stuff.
the problem is that the threads are in the pump body not the endplate, and there is little room to thread oversize. on the first stripped hole, i just ground a flat side to a hex head bolt and ran it through from the other side, with a nut securing it. i'd loved to have dome that with all of them, but other parts of the pump interfere. i ended up just re-tapping one of them to a 12/20.