I tried doing this exact same thing last year. The biggest issue I ran into was finding a triple pulley that would fit on the output shaft of a replacement motor --OR-- finding a replacement motor that could utilized the original triple pulley off the DLX 28. The Ariens DLX 28 pulley is 1-piece and made for a specific output shaft diameter and length. There are so many variations of motors and shaft specifications that it was like finding a needle in a haystack. I bought and sold a couple of motors with no luck and finally stumbled across a 2 year old unused Toro 1128 on Craigslist for a great price, so I bought it and sold my Ariens. Big power on a 28" ROCKS. Good luck and if you succeed and make sure to do a write-up with the details to help out others.
Toro 1128 HD PowerMax, 342cc, 16.5 ftlbs, 11+ HP
Ariens 722, 7HP single stage