If the male cats are allowed to fully mature, they develop massive shoulders and heavy jowls. The short haired guy on the right side of my photo is a good example. The long haired guy can hide his under all the fur, but he has the tom cat features as well. It will make their head look a little oversized for their body. Scruffy doesn't seem to have the same body mass, and I think you got him neutered while he was still fairly young. Your white cat looks like he has a mature tom cat head from what I can see in the photos.
If the cat is homeless, it should be fairly easy to get him on a meal schedule, especially if you get him used to coming when you call him and picking up his bowl after he has eaten. Once he gets used to you looking at him, you might get an opportunity to check out his back end to see if he is intact or not.
What does Mr. Scruffy think about the new guy?
