It doesn't matter, but are you SURE he's neutered? Some people will ie and tell you they are, when they aren't...
Playtime: In an enclosed area, load it up with toys, dust baths, and chew toys and put the two of them together. Be sure to stay close by to monitor the situation. A little chasing can quickly turn into a blood bath, so until you are absolutely sure they are getting along, never leave them unattended when they are together.
Car ride: Some people have success with putting both chins into a small cat carrier, then taking them for a ride in the car. Chins generally just drop off to sleep when they travel, or they are so upset by the drive that they tend to ignore the intruder in the cage with them. Drive around for half an hour or more each time, to be sure they are exposed to each other well. Then when you get home, try and put them in the cage together. Again, do not leave them alone. Monitor the situation, their reaction to each other, looking for signs of aggression from one or the other.
Smoosh method: I am not a huge fan of this method, but people have had success with it. You need a smallish cage, preferably a chinchilla show cage. You place both chins in the cage at the same time and leave them there for 15 minutes. You cannot leave them in their for hours. The point to this is a forced introduction, but keeping 2 chins in a small enclosure longer than that is asking for a fight to start, and it's also cruel. The cage needs to be safe, but it needs to be small enough that they are forced to climb all over each other to reach the other end of the cage, and it needs to be small enough that they can't 'fight. Once the 15 minutes is up, take them to a neutral cage, put a dab of kitchen vanilla just above their noses and around their tails, and put them in the cage together, once again, monitoring the situation.
Small cage within a large cage: This is my preferred method of introduction. Again, I recommend a show cage for this as a show cage should fit into almost any cage you would keep your chin in. If it doesn't, your cage is too small. When using a smaller cage, be sure that the bar spacing is safe and that a leg can't slip through and be caught. Place the more aggressive chin into the small cage, close it up, and put it inside the larger cage. Place a pile of hay in front of or on top of the cage, so the loose chin is forced to interact with the caged chin, in order to munch on the hay. Leave the chin enclosed for several hours, and I leave them overnight. As long as they have some hay to munch, they will be content until you release them. After several hours, let that chin loose in the cage, and put the loose chin inside the small cage, then place it back into the larger cage. Do this as many times as you need to until they either get along happily, or they don't.
Whichever method you choose to use, be sure that the cage you put the chins in together is neutral. That means completely cleaned and nobody's "stuff" in the cage. If you have hammocks, wash them. Put in a new wood house, new chews, new toys, piles of hay around the cage, and it helps if there are two hiding places -- two houses, two chubes, etc. That gives both chins a chance to retreat to neutral corners.
When you put them together, as mentioned above, put a dab of kitchen vanilla on the top of the nose in the fur, and around the base of the tail. It helps to mask the scent and make the new chin not so much of a stranger to the resident chin. You can also trim the whiskers back by a good inch to an inch and a half. This helps with dominance issues. It doesn't hurt them and the whiskers will grow back. Just be sure you have someone to help hold your chin, as they may struggle.
Sometimes, no matter how much you want a pair of chins to get along, it just won't happen. It can happen right from the start or it can happen years down the road. For every chin you own, you must have a separate cage. Even chins that seem to be absolutely wonderful with each other can turn on each other in an instant, and that spare cage could save your chin's life. At the first sign of a serious altercation, remove one of the chins from the cage. At that point, you will need to keep them separated permanently. Once a chin fights with it's cage mate, it will only accelerate and can lead to the death of one of them. Always be attentive to your animals, watching for sign of scuffles, i.e., fur all over the cage, fur missing from one or the other chin, nicks in the ears, severely barbered whiskers. These are the warning signs and should be paid attention to closely.