I owned a 1961 Corvair which I purchased used in 1967. The specifications in the owner’s manual did call for a difference in pressure between the front and rear tires. I think you are correct that the specification was 15 psi front and 26 psi rear. The rear axle was a swing axle independent suspension and the rear wheels did have a tendency to tuck in under hard cornering. A $15 investment in a camber compensator, essentially a spring that went between the two rear wheels prevented the rear wheels from tucking under too far. This became standard equipment with the 1964 model. It 1965, the Corvair adopted a fully independent rear suspension that eliminated the swing axles.
With the camber compensator bar, the 1961 Corvair I owned handled very well. I was careful to maintain differential tire pressure between the front and rear tires.