Before I knew about parrotforums.com, I used to do all sorts of things with my birds that are, apparently, not the go. Putting the same species in the same cage and expecting them to get along is one thing I've always done and (touch wood) never had a problem.
Of course, you need a cage that's big enough for both birds to fly and also for both birds to have their own feeder, drinker and toys (saves arguments over who gets what). You can foster togetherness by putting one short perch in the highest part of the cage. That will encourage them to roost together and, hopefully, sort out their differences.
You will always get the odd peckfest between birds, but I don't think there's any reason to expect out-and-out fights to the death UNLESS you're adding a new bird to an established bird's cage. In that event, you'd have to decant both birds to other cages, completely redecorate the communal cage and then introduce the pair to it at the same time. So long as there's room to fly and escape from conflicts, things should percolate along OK.
