Joe,
With regard to rotor shafts, I can tell what I've learned and what some other blackhawk pilots told me when they were building their "from scratch" RC helos.
I tried 1/8" stainless and it bent from the torque right where the drive gear was mounted, but your masts are "free wheeling". Titanium is tough, but it has a "spring" whip effect depending on how long the mast is. Titanium is great for drive trains when carrier bearings are used. It may be ok to use titanium in shorter masts, but again I'm not sure how long your tandem airframe gyro masts are. If you want, I can send you some titanium rod that I did not use it's a bit thicker than 1/8" but not much. No charge of course, because I know you would use it for something.
Regarding the speedo cable, I assume you're "synching" your hubs? If so, maybe try the titanium as "synch drive shaft" with light weight bevel gears and 2 or 3 carrier bearings. Some speedo cables have lubrication inside the sheathing, but some torque is lost through the flexing of the cable inside the cable cover.
I also got some extra carbon fiber sheet and I've learned that if you sand it and glue 3 layers it makes good pillow/bearing blocks for small bearings, yet keeping the weight down. Again no charge. I got alot of raw materials floating around. I think my wife is worried that I will bring it home to Illinois and clutter her house. The blackhawk pilots used 4130 chromoly tubing for rotor masts. I've been looking for tubing that small, but I may need to use solid chromoly.
Let me know if you want the titanium and CF sheet pieces.
Dave