GMK space bars (from the recent buy) have but one pair of outer stems, and the distance center to center between them is 100 mm, like on a Filco or a Cherry MX-3000.
SP space bars and EK space bars have an additional second pair, with a distance center to center of 80 mm from each other, like on an FC200.
There were Leopold space bars with a distance of 85 mm, so for these keyboards neither will fit.