Not sure on the manifold, but in taking a second look at your stands...I think you should add vertical supports in the middle. Six feet is a long span to go unsupported, especially since it looks to be 2x4s (vertically they are plenty strong, but horizontally, not so much...especially with almost 1 ton on them). I can see your stands potentially sagging in the middle and causing problems over time. Hope you don't take my comment the wrong way...just trying to hep.