That super scraper attachment might be tough to work if you have a tracked skid steer, although i cant say that out of experience, but it works best when u swing the machine side to side to scrape up the tile

The problem with the superscraper is this: It will not scrape any yellow glue. If the yellow glue is gooey and sticky, pieces of tile are going to stick all over the floor, making cleaning the floor a little more difficult. We take the dust from our shotblaster and sweep it around on the yellow glue and it takes the tackiness out of it.
The straight blade scraper will eliminate alot of that.
I would not agree to 70% of glue removal. I would say all or as much as comes up with tile. I think it is hard to qualify 70% of glue removal.
If you get them to agree to all, then shotblast the floor.

NEYC, I have looked for the attachement you refered to for the skid steer, but cant find it. I would be interested in picking it up if it will work. After talking to the GC some more the last few days, as long as I can get a majority of the mastic up, then just the friction from the loader, JCB, lifts, peoples feet, etc should be enough to clean the floor of the majority of the mastic before the new carprt goes in. They have done a bunch of these stores before and said thats what has been done before and worked well.

He also said tonight that they wanted an alternate on leaving the flooring in place and putting the new floor down on top of it. He suggested not doing this, but he can only give them what they ask for. I told him I cant gurantee the condition of the old floor once I am done, and that more than likely it will be pretty much destroyed.