Hey, I was a lifeguard for years and a judo player. It means he will be comfortable in the water and should be calm under pressure. You'll probably need to be very vigilant about him overexerting himself though. In particular he needs to get out of his gear before exiting the water. A weight belt is a good idea since it splits up the weight and he can hand it up first. If you are doing shore dives, he should also have help getting it into the water.
As
@Eric Sedletzky said, get a large/long steel backplate and a big steel tank. This will get the lead he needs to carry on the belt into a reasonable range, plus I'm sure he'll be sucking air at the start. Although given his background, gas consumption might level out pretty fast.
I guess from your profile this is warm water diving? Someone this big, especially a former lifeguard isn't going to be bothered too much by mild cold. I think you can find a 3mm shorty in his size? It should be good down to 78 degrees, maybe 76. If you have 80+, just a rashguard.