The Terwilliger book (that's the one you're referring to) is a great resource, and pays for itself the first time it assists you in repairing or maintaining your clock The bad news is that it exponentially increases your interest in these clocks, at least it did for me. In the few months since ordering the book, I've gone from owning a single Kern to about twenty torsion clocks, all of which I've been able to renovate with the help of that book and some kind folks here on the forum.
Having said that, it's certainly possible to build a suspension unit without the templates in the book, but it will take much more trial and error. You could measure the distance from the hole in the saddle (where the pin screw for the top block attaches) to the location of the bottom of the hook on the pendulum when the pendulum is held or propped up JUST above the base of the clock, and that would give you a starting point for spring length. It will still, in all likelihood, be a bit too long, but you can always nibble off small bits at a time until the pendulum suspends freely. You can't add MORE spring, so much better to start too long. You'll need to remove the suspension unit and the bottom block each time you trim a tiny bit of spring off, then test again. I usually have to do that at least once even with the book's templates, as I tend to be overly cautious about cutting the spring too short.
Also, the distance between the fork and the top block is very critical, and the templates really just provide a starting point. Generally, they're pretty accurate, but each clock is different...if the anchor pin is bent slightly forward or backward, that can change where the fork is the happiest. Again, small changes and trial and errror. Gauging the amount of pendulum overswing in relation to total rotation will tell you if the fork is mounted in the best spot, along with the how easily the fork and anchor "flutter" when in the center of the travel. In my (still limited compared to many here) experience, when a clock is setup for a good ratio between power (overswing) and total rotation, the fork/anchor will flutter a few times when the anchor pin is vertical, the fork is pointing straight forward (assuming the pin is not bent), AND the minute hand is pressed to manually advance it. It should never flutter on its own.
Hope that adds a bit of help. Personally? Just get the book. Completely worth it.