I moved mine back a couple of inches, still on the frame rail. 65 Barracuda 340, TTI headers. Then shortened the front/rear line the same couple of inches and fabbed new M/C lines. Of course, you'll need a double flare tool.
There's no single correct location; just put it wherever it clears everything. The valve location varies from one year to the next anyway. At least, the OEM locations of my 63 Valiant and 65 Barracuda were 2-3 inches apart.