Well, the best way is allow them to meet outside Deliloh's cage. If you put Gilbert in the cage right away, your older one will get very angry and feel like his space is being invaded.
Put them next to each other in their cages and let them play on the floor together. Some behaviors will be normal like rumble strutting and mounting. It is a way to assert dominance.
If they start biting and really fighting each other they should be kept seperate. It can take up to 9 months to see if two males will stay together peacefully so it might be a little difficult to introduce them.
Here is a video of rumble strutting.
http://www.youtube.com/watch?v=ACQyr1l6kmg