The original was made by Kelsey Hayes and it worked perfectly. The internal springs were selected to work with the EB weight distribution. There are no others that were or are made that way. When I rebuilt mine, I bought a bunch at local JYs. None had the same springs. That included those for cars, vans, and pickups made by all the big three. Some of my internal parts were corroded and replaced with the donor valve parts. Others came from Muscle Car Research who makes soft parts, gaskets, and instructions. Once done my brakes work better than ABS. The after market valves are one size fits all, except they really don't. And they don't work as well.