The longer barrel is a plus. Most of todays high performance sabot slugs are designed for long barrels. I would consider 22+ the minimum for full utilization of their benefits. It seems 24in is the standard in dedicated slug guns currently.

The cantilever is also a must have for holding point of impact with a switch barrel gun.

Short of getting a new dedicated slug gun I don't think you can go wrong with that setup. Keep in mind that you should be prepare to spend some time and money at the range if you want to get the most out of your setup. Try a couple of different sabots to find out what shoots best in your gun. If would like advice on sabot choices feel free to ask...