No I didn't,
I replaced the front drive shaft with the Ext shaft from Cobra Transmissions.
I was concerned about the extra tension on the joint with the two discs.
The guys a Cobra were amazing and it was delivered to Australia within 3 days with the DHL $77 option. It was a little hard to install being that it's longer. It misses by about 2mm, but a little stretching of the engine/gearbox mounts and pop in it goes.
Would love to hear how you go if you try the dual discs.

Replace the Guibos first, chances are that is your problem. Do not start with transfer case chain slack. Guibos are the cheapest fix, do those first and see if the problem persists.

I'm going to climb under there this weekend and inspect, I'm getting a hum and starting to get a drivetrain vibration. At my mileage I'm assuming the guibo's are done and the vibration is the center bearing going out, or maybe the rear CV?

Yes, I'd rather not introduce more flex into the system with a second disc. I'm thinking I'll get my friend who works at a machine shop to make a solid aluminum disc for me and I'll buy some longer grade 8.8 or grade 10 bolts.

The flex has certain torsional characteristics designed to work with the stock driveshaft over the range of rotational speeds the driveshaft sees. Do not put two flex couplings in it.

That's why i was thinking an aluminum spacer instead...