I just got it done and I talked to Jenny at Sew-classic. She also sells a belt guard for around $7 or $8 with a bobbin winder. It, too doesn't come with screws. Since I don't have a 15 clone for parts, I used the old throat plate screws - then replaced them with new.
The Singer motor mount screws are larger so don't fit the hole or the new belt guard holes don't line up - either way...