One thing I'd suggest: check your tire presures HOT and not COLD.
Your tires are hot most of the time (when is use), so it makes sense to get them up to temp before checking.
I'm running around 28-30 psi hot in my street car with radials (not a Spridget......it's an MGB).
As stated, those old tire pressure specs are for bias tires and not radials. Bias tires always run less pressure.
For comparison, Spridget racers who run on the latest Hoosier TD bias race tires typically run around 26 psi (hot).
On the other hand, those of us who race on DOT radials run much higher. I run around 38 to 40 psi (hot) in my Toyo 888s.