I had the Juki 98Q on a Grace Pro frame once upon a time. Loved it. At one time, though I have a feeling he's no longer doing this, there was a man down in OK. that stretched the Juki machine to 18 inches. This is what I did and I never had a lick of trouble with it. Sold it when I went to the Innova.
For the Grace frame if you get it, you might want to beef up the poles as they tend to bow. I slipped galvanized poles right over the original poles and then screwed them into the poles. I also replaced the rails with a metal type found at most any home tool store like Home Depot, Menards, etc.