About the only thing to limit mixing brand names of treadles and heads is the size of the flywheel on the treadle and the handwheel pulley on the head. Since you’ll be providing a custom top for the unit, the limiting factor of head fitment and pulley alignment between different manufacturers will not be a consideration.
The pulley sizes (flywheel & handwheel) are only a minor limiting factor at that. But consideration should be given for matching the two well enough to allow for comfortable treadle action for the needle speed desired. In other words, a large 16-inch industrial flywheel used on a head with a small 2-inch handwheel may result in stalling and lack of momentum from treadle movement needing to be too slow to get a good rhythm established.
For your Singer 128, I would lean more toward the normal flywheels in the 10-12 inch diameter size, and steer away from the 16-inch flywheels as are common on the Singer industrial treadle stands.
CD in Oklahoma