Stranger things have been done, it could work. You should be able to hog most of the material by hand and use the fixture for the last bit, but it will take some time and you'll have to nibble at it. I've seen guys grind hardened lathe ways by mounting a grinder on a sled and running it up and down the less worn tailstock ways. Those jobs ended up at a couple tenths of thousandths over several feet.
