Here are my thoughts:
Letís start with blanks that have spines verse those that do not have a significant spine. There are companies that taut having rods without a significant spine. To my knowledge there are a few methods of accomplishing this feat. 1. The use of a lot of transverse direction graphite (weave pattern). 2. The use of a helix core or multiple helix cores. 3. Wrapping the cloth in a spiral along the mandrel creating a spiraling spine. Iím sure there are other methods of which I am not aware.
Although a spineless blank might be great from a rod builderís point of view, it would be a little lacking in casting performance. This would be due to the additional weight that results from the transverse wound carbon. This extra weight would amplify tip oscillations. To achieve ultimate performance a blank must have the maximum longitudinal graphite while maintaining sufficient transverse graphite to assure required hoop strength. We must rely upon the experience of the manufacturer to achieve the requested characteristics of strength, minimal weight and maximum dampening.
A high performance blank will have a spine. The amount and locations of the spines will vary. The optimum case is when the primary (or most significant) and secondary spines are at 180 degrees from each other. In this situation the guides can be mounted at either 0 degrees or 180 degrees. For pure casting (multiplier/conventional), I would mount the guides on the inside of the curve generated by the primary spine. For fish fighting purposes, I would mount on the outside of the curve.
There are DVDs that demonstrate finding the spine on a blank. These usually depict bending the tip of the blank. With modern day composites tips there can be variations in the location of the spine and the spine can shift along the length of the tip. With large surf rods and tournament rods, it may be a better practice to start checking for the spine at least one foot from the tip top.
Often the primary and secondary spines are not displaced by 180 degrees. 150 to 210 degree displacements are not uncommon. The worst case I have seen was 90 degrees. When the spines are not at 180 degrees to each other I make a compromise. If we assume the primary spine to be at 0 degrees and the secondary to be at 150 degrees, I would probably mark the spine at 350 to 355 degrees depending upon the significance of the secondary spine (not an exact science).
The guides should not be located at 90 or 270 degrees from the spine. At 90 or 270 the higher frequency (more rigid) axis of the blank would be in line with the guides. This would cause the blank to bend to either the left or right during a cast. This results in undue axial stress along the length of the blank. In time the fiberglass components of a rod will break or weaken. Another way this may be viewed it to consider the breakdown of the fibers that provide hoop strength. As the hoop strength decreases, it is easier for the blank to take on an oval (softer) shape.
For the handle, I usually put two soft bound books on the floor and straddle the handle between them. A downward force easily identifies the spine. Now join the tip and handle paying attention to the alignment of the spines. Did the tips spine shift a little? This may be due to improper alignment of the ferrule or a slight bend in the handle and you may need to make a compromise. Simply rotate the handle in the ferrule a few degrees until the tipís spine returns to its original position. This method has proven to me to be a little more effective than sighting down the blank.