Fitting the head is not so bad once you develop an eye for consistency. Using a tape measure to achieve initial length, width and depth is good start. A set of outside and inside calipers is even better. Take your time with a rasp. Belt sander is often way too fast and imprecise unless you use fine grit. The minute you can slide even so much as 1/2-3/4 inch of the handle into the eye you'll have a perfect pattern for matching to for the remainder of the fitting. If you're at all nervous practice with pieces of softwood (pine, basswood or spruce) until you get comfortable. A properly and carefully installed handle that sees only recreational use is likely to last you the remainder of your life!
Shrinkage is inevitable even if the handle appears to be bone dry at the time of install. In days gone by folks used to soak the heads in water overnight to ensure they weren't loose during use but I've taken to applying drops of oil on the eye on an regular basis. It soaks in quite nicely and (presumably) makes the wood less prone to shrinkage. Started doing this about 30 years ago and have not suffered from mid-winter 0 humidity loose heads anymore.
