I used those Croaker Firestone bias plies on my Cadillac for a short time. I kept them inflated to 32psi. Car weighs 5000lbs with me in it.
You should know that those "Firestone" tires from Coker are made in Vietnam on in worn out, 70 year old molds and will be next to impossible to balance properly. At low speeds or in parking lot car shows I guess it doesn't matter so much.
If you plan on driving regularly, you're next set of tires will be Diamondback radials.www.dbtires.com
The tires below are 700-R15 Yokohama radials.