I don't have any experience with the Jungle Jack, I use the Mojack EZ but my mowers aren't going to be as heavy as your Scag Mower Lifts | Hand Trucks| Lift Accessories | Hand Truck Accessories | MoJack I'd check on the XT or the Pro. The EZ only lifts 300lbs,The XT lifts 500lbs and the Pro 750lbs.
I lift a 48" and a 44" ZTR with the EZ and it has no problem with either.