I had 2 intact males that NEVER got along, and were kept separate from each other, always.
I didn't see it mentioned anywhere, but make sure these 2 have been neutered. (not seeing it mentioned may be MY lack of 'seeing it,' not that it wasn't here)
There is no scientific basis for believing that neutering changes behavior. On the other hand, there is science based evidence that neutering increases the risk of many cancers and other physical maladies. We've had intact males who got along just fine, with never a fight for their entire lives.
@donc I forgot that ! thank's for reminding me. On my website (not the pedigree one) is a piece I wrote some time ago - its called Basenji Boys Have A Rutting Season Too - and many people have been kind enough to say they found it helpful.
Great quick read! Highly recommended.