I have a deaf dog, although she's been deaf from birth, so it's not quite the same as your situation. However, I didn't meet her until she was about 4 years old, and have still managed to teach her new signals.
Agree with the poster above - big clear hand signals for sit, stay etc, reinforced with your voice and lots of praise. We use a 'wave' or a clapping hands gesture in place of 'good girl' and make a big happy hands gesture when she does something right - so with your dog, just start using your chosen hand signals alongside the voice signals. And it's important to do this all the time from now on.
I've found that my other - hearing - dog now responds to the hand signals without me speaking so it's clearly possible for them to learn new hand signs.
As for recall - obviously, you need to rely on the dog looking at you. We use a single hand beckoning gesture, or, if the dog is far away, I do star jumps and wave my arms over my head. People must think I'm bonkers if they see me do this, but what the hell. Once the dog starts to come back, I jump around waving and make a big 'hooraaay' gesture, then give her a massive fuss when she gets to me.
To get his attention if he's looking away from you, just touch him gently while speaking, then praise him when he looks. You'll need to rely on your dog checking in on you regularly once he is deaf - and this might not be too reliable, so be prepared for that. Our deaf dog is prone to going off exploring, but will come back to where she last saw us. So if we lose sight of her, we stay still until she looks at us. Because if we've moved off out of sight, she panics.
Oh and be aware of spooking him by coming up behind him in the home if he doesn't know you're there. I've got into the habit of constantly touching my deaf dog whenever I walk past her, just letting her know where I am at all times.
Again, I would just do this all the time from now on alongside your voice commands, so that if / when your dogs hearing does eventually fail he will be used to the hand signals.
Consistency is the key here. But your dog can learn new signals. Good luck.