I use tubes on 7 inch rims and go down to 6 psi with no problems

Whats up with the WOF and rego rubbish
Not may good grade 5 trucks will meet that
I was looking forward to coming down but you will have to count me out now as mine lives on a trailer

A welded rear diff is the way to go at minimal cost as well.
Put a decent set of tyres on and it will leave a quad for dead.