Hello All,
I run 235x75x15 radials on my 64. I find the ride somewhat stiff at 35 PSI. So I recommend 30 - 32 PSI. The ride softens and the handling doesn't seem to suffer. I base this partly on trial and error and old road tests in Motor Trends of this era. Admittedly, this is not my daily driver. I suppose if it was, I might be more scientific.