Once the dog is comfortable with you coming up rubbing his ears and sniffing around his head (without flinching away) it’s floor play time.
NOTE: butt sniffing. The big dog doesn’t sniff butts. The #2 dog is free to.

Fart on him to give him a snoot full. Really, the dog will love it.
Work the dog into a comfort zone where he doesn’t flinch or shy away if you try to hold him tight. Sniffing while you do this. This will take a little time to develop. Make some other dog noises. Guttural, from the throat. And high pitched me me me noises.
Rudy loves this and will start singing back to me.
Be prepared for a lot of licks. Accept them for what they are, his expression of love. Just keep you mouth shut and wash your face later.
When you can firmly hold the dog without him struggling you can start to erase the fear of loud noises. His acceptance of your tight embrace shows he trust you and is comfortable. While holding him, have someone clap their hands once. The dogs frantic reaction must be anticipated and you must immediately start to comfort him with rubbing, dog noises and sniffing. Don’t try to hold them back if they want to bolt. Just work back into where you can hold them again. Don’t you jump at the sound. That will reinforce his reaction. Remain calm and, in his eyes, unafraid. Depending on the initial reaction you may want to wait a few days to try the clap again. Learn to read the dogs mood. Slowly work up the number and sound level of the claps until you see the dog look up to you for your reaction to the sound. If you don’t react he will learn no to also.
PS
Farting on the dog.
I was on some powerful antibiotics for a few weeks. Antibiotics nuke the good and bad germs in you body. Particularly your stomach. I was generating gas that would clear an auditorium.
I was sitting on the couch with one leg on the armrest. Rudy comes up, puts his head on my lap for some head scratching. I had to let one rip. Halfway trough the first sniff his head jerked back and he gave me a look that said “D@mn Boss, What did you eat?” I laughed so hard I almost dumped in my pants. Rudy took a few more tentative sniffs, from a distance, and then went in the other room to lie down. I felt sorry for him and opened the sliding door to air out the room.