My comment about the PSI looking low was based on my experience with my 35U not based on any knowledge of your tires and rig. I should have qualified my comment. In any case, I think I've figured out the 70 lbs PSI.
Here's a link with a similar discussion that links to a chart:
Hankook 245/70 R19.5 inflation chart - iRV2 Forums
Looking at the highlighted line on the linked chart (AH11 70/245/19.5 which may or may not be your tire), go to the right hand section, which is in kilograms for weight. It gives PSIs in () for various axle weights (kg) based on two tires per axle.
Your front axle is 6,000 lbs which converts to 2,800 kg. Looking at the table you see that it stops at 3,095 kg and a minimum inflation of 65 lbs. Adding Tireman9's 10% safety factor would bring you to 71.5 lbs.
Your rear axle is 11,400 lbs which converts to 5,171 kg, but you have four tires instead of two on it so you need to divide by two. This gives you 2,585 kg, which is also below the minimum kg @ 65 lbs, or 71.5 lbs with the 10% safety factor.
Your GVWR in kg is 3,175 front, 6,123 rear which, after dividing by two is 3,061 kg rear. According to these weights, the table PSIs are both going to be somewhere between 65 and 73 lbs, again close to 70 lbs. Note that the OEM tires on which the "badge" is based wouldn't have been Hankooks so there's going to be some variation.
If your tires are a different size than 70/245/19.5 you'll need to go to the appropriate line on the table.
And, I agree with the cheap handling fix. If you have the right chassis it's a no-brainer and could save you thousands.