.........
This truck is used for 90% farm truck at 25 mph or less on the dirt roads of my property. The other 10% highway at speeds of 45mph or less, usually 35, for short jaunts to the market or fishing up the road a ways. Was considering using these on the back and some like new 6.50-16's on the front.

I agree with what Leo said but if the quote above is correct then I think you would be alright to drive it until you can put some pennies in a jar for two nice rear tires...... or, as suggested, find two that will work at some tire store. Around here a fellow can get a pretty nice used tire mounted, and balanced, for $20.. no more than $25.
That is a cheap price to pay to feel safer going down the road.