I've cabled quite a few codominate eucs just like that here in San Diego county to prevent them splitting.
EHS steel cable n throughbolt hardware of course.
None of that dynamic cobra synthetic crap......
The tell tale sign of bark beetle's little 1/8th inch holes riddling the branch structure, generally starting at the top and working its way down.
I use a spotting scope to confirm its presence from the ground.
I suggest removal regardless of what's killing it to keep whatever it is from...
I'd recommend using a redirect block at the LZ just to be safe.
Tensioning with a mini pulling 90 degrees off the main line'd probably work well if you stay under 500 lbs.
A 7/16ths wire rope oughta do it.
What part of the country yu workin?
Wire rope's your best bet IMO.
I've speedlined big stuff 150 feet and even with 3/4 inch bull line, it was a sloppy wobbly anything but a straight line affair.
Haulback control line's a must even with wire rope, unless you have a huge landing zone you can tear up.
Best of luck gettin the job...