I should have been clearer - some of the really expensive snap on blade clippers can do a body clip; but on a horse that is clipped regularly, like a show horse kept under lights. We used to use them to do the head and neck clips on foals.
When I worked at hunt/show/event barns, you always had two sets of clippers - the big, heavy duty body clippers with the tension screw like I linked to and a smaller set for trim work. The smaller set was sometimes a just an ear and head trimmer; the better arrangement was if the smaller set was the snap on blade type like an Oster A - 5. You could use them for legs, the head and any touchy, ticklish areas, not just ears and muzzle.
If you clipped your Cushing's horse frequently, before the hair got long and coarse, you'd probably be okay with the snap on blade type.
But if the horse has a lot of coat, you want the type I linked to. It's also *tons* faster.
Also, the snap on blade type, even with a 5 blade, clips closer than the body clipper, not necessarily a good thing in the middle of summer.
And bless you for going to all this work to make this horse comfortable.