overload springs and tire height

[oldcarbuff]

I've got two unrelated questions:

first, my dad just bought a 70 long fleet (my 67 longstep talked him into it). On my truck, the overload springs are long, sort of half leaf things that are at the back of the frame. His truck has overload springs that are a second set of coil springs mounted in front of the normal coils. Were these both factory? or is one of these a do-it-yourself project at some point in history? His rides a bit stiff, and he has debated taking the extra coils off.

Second question: my 250 I-6 is wound up at about 50 mph. My back tires are 26 inches tall--how tall should they be? Dad's tires are about 27 1/2 tall, although they are both 75 series. My tires are nearly new and I hate to toss them, but I also don't want to float the valves trying to get on the highway.

Thanks

OCB