Main evidence is that near and far UV CD and trap fluorescence is unchanged. This is useful and consistent with no major unfolding, but is not high resolution. More definitive would be X-ray crystallography, but much more work and has some limitations of its own. Note that the correctness of the DNA sequence and the mass as determined by mass spectrometry addresses whether or not they had the correct polypeptide, not whether it was folded properly - although on relooking at the wording of the question, it could also be read to include this.
Limitation is that changing amino acids often effects other aspects of catalysis as well.
Can see this as non-additivity of the two Arg substitutions. Just binding tightly to ras with extensive contacts does not help. The switch regions are called this because they are in different conformations between the GTP and products forms and so GAP can help by binding to and stabilizing the forms near the transition state. In particular Gln61 is mobile without GAP but aligns properly for catalysis when GAP binds. Kd-d is derived from the concentration dependence of the slow phase in a more conventional way.