Maybe my Henry gets a buddy- how is everyone introducing dogs to each other?

We had a Chihuahua and a Lab. After the Chihuahua passed away the Lab started moaning at night. He was missing his buddy! So we went to the SPCA shelter to look. When we found one we liked we took the Lab out to meet them in the field by the shelter. First one was another male Lab. No go. They didn't want any part of each other. We went back again and met "Rock" a pit bull...no go again. Third time we met "Ziggy" another pit bull cross but a smaller and younger male version. They immediately took to each other and loved each other until Leo crossed the rainbow bridge. Just before Leo left us, we picked up a stray off the middle of the road. They do okay together but it's not the same relationship Ziggy and the Lab had.