Hello & Welcome
The AMD65 rear trunnion uses two long rivets just like a fixed stock, so if you didn't order rivets yet, get a set for an AKM fixed stock.
You will still have two extra holes in the receiver (if it already has them), the front holes for the fixed stock mount won't be used.
It's hard to give you an answer about riveting since I don't know what tools you have or your skills.
But people have made a simple plate with a rivet head dimple to rest the already formed head in, and used a punch that they modified with a dimple and just beat the new head into shape with a hammer and that modified punch.
If you can remove the barrel to rivet the trunnion into the receiver.
Being careful and getting the pin notch in the barrel lined back up with the hole should keep you close to the set head space to be safe.
I'm not sure what a 4x air rivet gun is, so can't comment on that