the gun looks nice, bottom metal does look like original oberndorf style, i think guns were confiscated years ago by the zimbabwe govt, bolts taken out and all dont know if this would pertain to your gun ,but could be why the bolt doesnt match i think gregor woods writes about this in his book , martin hagn has one for sale. yours looks like an early gun 1920,s.
dont know of a reason why the numbers would have been, changed...paul