The SHO was built to be an MTX only car. When Ford decided to make an ATX, they had to make some extra room for that big, fat transaxle to sit behind the engine.
As a result, the engine moved forward and the Front Engine Accessory Driveline (FEAD) was re-designed. This means that the ATXs and MTXs have different pullies, exhaust manifolds and engine mounts.
A lot of people will tell you that you should use the ATX FEAD if you can. Since it's a self tensioning-single belt system, it may require less maintenance, but I think the MTX FEAD is more well suited to your application. Especially so because you will not be using the power steering pump (except maybe as an idler pulley for the water pump?...).
Anyway...that's why there's "MTX only" on certain items that seemingly have nothing to do with the transmission.