Remember that, when thinking about the loads that the rotor imposes on the mast, you must consider the whole picture. It's misleading and dangerous to think of rotor drag pulling straight aft on the masthead, while ignoring the much large force of LIFT (which pulls straight up).
The rotor, in reality, creates just one force, not two. The standard term for this single force is rotor thrust. For discussion purposes, we artificially break this single thrust force into two sub-forces, lift and drag. We must always consider them together.
The rotor's thrust in cruising flight pulls up-and-back at an angle of 10 degrees or so, and the mast is angled so that, in this condition, the mast is subject to pure tension (it's many times stronger in tension than in bending). During flares and slow flight, the rotor disk's aft tilt is greater than ten degrees, and the mast then experiences an aft-bending load.
Bumblebee and Gyrobee gyros were designed around a mast that violates the Bensen aft-raking rule. These gyros' masts are perfectly vertical relative to the gyro's horizontal axis. Therefore, they are loaded in bending continuously. For these light gyros, however, the bending loads are modest compared to the strength of the mast (especially a double 1x2) -- even without the old "forestay" cable.
The cable on my Bensen scratched the top of my shiny new helmet. Aggravating.