You'll need to do some more diagnosing. Could be a bad fan clutch, could be a clogged/dirty radiator (flush may fix), could be engine related issues. State Automotive in Midvale is very competent with cooling system work and knows the BJ74 well too.
We would love to help @ Cruiser Outfitters. We not only stock the OME for the 7x Series (including your BJ74) but we are super familiar with them too. We've sold/installed dozens of these kits for the non-US 74 Series and I have personally owned a handful. I was just above your hours (well AF...