harness safety belts

I need to install safety belts in the back of "Beast-Lee" (for short trips with my older kids) and was wondering about putting in harness safety belts. Is there a universal type belt that would work or should it be a defender specific safety belt? I am also wondering if it is possible to install the safety belts first (don't have the bench seats yet) or is that putting the cart before the horse. Should I have the seats FIRST then install the belts? My kids are desperate to go for a spin. I know it's not ideal to have kids in the back but they are older and trips will be short (school, going to the beach down the road etc). Any advice or words of wisdom will be greatly appreciated.

Contact Stephen at SafariRover on this board. He has the seats and the belts for sale. Didn't your truck come with the jump seats?

no. the previous owner took them out and "stored" them. He is a professional basketball player and I was told he stored them in one of his many homes - can't remember which one and is too busy to hunt for them. I got this defender at a pretty good price so won't complain. Thanks for the lead. I will cantact Stephen.