HI there and thanks for the post
This is a quick one to answer as you are doing everything right. All you have to do is use the same method you have been doing with the recall but in a more controlled setting
Do the same thing but make do it in your back yard with another dog. Get the dog to sit a few metres away from your dog. And follow the same principle starting with a short lead and building up the right behaviour.
As he gets better and better give him more and more lead.
After he gets well behaved with another dog and so on. Once he is really well behaved give a try with a couple of dogs.
For a start it will be easier to keep the other dogs on a short lead but as the training goes on have them more and more off lead.
Keep up the great work and let me know how things go
Todd