I would recommend separate enclosures for a couple reasons. One is feeding time. one or the other would need to be out of the cage while the other animal eats. I have seen people lose snakes by one starting a meal and then becoming the meal as the larger snake starts on the other side. Also I would strongly recommend separate enclosures if they are not similar in size. Also its harder to monitor the waste of your animals (one animal could be backed up and you wouldn't know for some time). I have done it quite a few times with smaller snakes (always the same size and species)and always regret it.

My two cents..

Thanks,
Ed