Years of working with machines, gearboxes, and pto shafts has taught me that if you put "rounded" teeth engaging on "new" teeth, failure will result. The only question is the amount of time. Since there are irregularities in the mating surfaces you also introduce the elements of vibration and possible shedding of metal fragments. Neither situation is desirable if you intend long term operation. I went through a similar scenario in a farm truck. I first tried to rig it "on the cheap" with used mismatched recycled parts. The third time I fixed it, it cost a new input shaft, several bearings, and a new output shaft. It was in a pulling truck and under severe load, but the principles involved are identical. Good luck with whatever you decide.