What can you [we] say? Incredible? Great Re-use of Materials? Terrific Design?
Most impressive to me, entire gearbox turned not by hand, just two fingers! That's both holding sizes and alignments to a very high degree; not in a production facility, on his home built machine tools.
Only one suggestion.
Upon quenching, keep the part moving. Air bubbles insulate, making heat reduction less rapid or uniform. Plunging in that cylindrical bath would be sufficient.