You'll find that the beam wrenches are the ones that hold their accuracy. I have beam wrenches all the way from inch pounds to 400 foot pounds. No springs or moving parts, just a torsion beam.
As you work, you'll develop a sense of how tight a given fastener should be tightened. Most aren't particularly torque critical. Most pro mechanics don't bother using a torque wrench on them because they know through experience how tight they should be. They do use one on the critical stuff.
One of the best things you can buy for these bikes is a set of metric T-handle allen wrenches. You can tighten the small fasteners adequately without worrying about twisting them off.
10 Duc Streetfighter S (black)
67 Triumph Bonneville TT Special