Do you have my book? Go to page Appendix E-4 in the Transistorized Ignition section, bottom left image. You can see the termination of the throttle cables there, and that is the OEM version arrangement for [my] K2. The bottom right image shows how they pass under the rubber tank stanchion at the front left side, below my finger.
There's also a "do not do this" picture on page IV-17, showing how I found a return cable routed in a K4 I tore down for the book. That cable had also developed a significant crimp in the sheath, right by the throttle cable mount on the carbs. Another "don't do this" picture is attached below. It shows the return cable coming up underneath the frame crossmember, which puts a real drag on the cable. This one was a +3" longer return cable and the owner was trying to "use up" the extra length somehow, which resulted in a throttle that would hang at almost any speed from a lot of friction in it.
In an old K1 picture I have (photograph, genuine Kodak type) it shows the forward cable coming down from above to enter the forward mount, like you have it in the image above. This later changed, and somewhere I have a Honda drawing of "Throttle Cable routing for CB750K2 longer cable" that came out in late 1972 because it changed when the return cable got slightly longer so that it could route underneath the coils along the frame. The issue at that time was (IIRC) that water was following the return cable during wet-weather riding and it dripped the water onto the coils, causing [potential] sparking from coil wires to the frame or tank under the fuel tank, a non-desirable situation.
I got to experience something like this firsthand in 1986 when riding back from Texas (Midland) to Denver and ran into heavy rains about 9 PM on the way. I didn't have the Vetter Lowers on for that trip, and my legs were getting wet (dumb...) as the spark from the #1 coil was intermittently biting my left leg, just below the knee...that was really an annoying night's ride.
