the original manifolds don't necessarily need the heat flapper to work, as long as it isn't stuck in the "heat" position, that creates some really weird issues. I ran my truck for 20 years with the heat riser broken and had no idea I even had a problem. However the aluminum intakes used with fenton (or whatever sort of header you may use) needs heat of some sort. If you use water you need to have two lines, you need a constant flow through the heat plate area. of course it isn't going to heat the entire manifold, but it does heat it enough to make it run good. but if you only have one line that won't work at all.
