spine

I am starting my first rod and building a 8'6" 4wt 3 piece. My question is locating the spine on the butt end it is pretty heavy material and the traditionat way of rotating it without as much bend is hard to locate it. Should I just eye ball it and then align it with the rest of the pieces or will this, if I don't correctly find it cause it to rotate? Or is there an easier way to find the spine on this section. Thanks in advance.

If flexing the rod section doesn't show a pronounced spine, then it won't matter how it's aligned and shouldn't effect casting.

I would eye ball it and align it for straightness with the rest of the pieces.