Milt...
Yes - 21g seems unlikely. However NB at what the 8g / 12g ultimate was for - empty weight 7000lb, MTOW 12000lb.
Shorten the wings, take out a lot of weight, light fuel load (in fuselage tanks), and suddenly your ultimate 'g' increases by a large amount. Clearly it will take someone familiar with the structure / design to know what should fail at 12g / wing bending relief aspects etc. But I would not be amazed to see something approaching 20g not resulting in major failure.
NoD