Zimm
The cardan shaft would be of no use with a c&t, without it maybe. On a linked suspension the pinion doesn't move much when the suspension cycles. At least from what I know and understand, maybe it does with radius arms though? I don't think so though. Now with leaf springs, the pinion is going to move a lot and that is where a cardan shaft is best suited, imho.
Here's the deal on the c&t. On my FJ60 I put in the MAF shackle reversal kit. With that kit in stock configuration, even with the lame wedges under the leaves, flexed up the truck and front prop shaft fell apart! No idea how people are running that kit and not having that problem, the first time I flexed the truck after the kit went in the prop shaft moved so much due to pinion rotation that it was simply not going to work. After the c&t on that truck, albeit SUA, no more problem. Now that was leaf springs and has nothing to do with the 80, however, after the lift, new springs and c&t that truck drove better than any other leaf sprung truck I have ever driven. 4wd in that truck on dry pavement at 60mph and it was so smooth you could hardly even tell it was in 4wd. After that, I am a huge fan of c&t's. Krazytoy is a good buddy of mine. He had an 80, I drove it several times. Before he c&t'ed his front axle the truck had vague steering and wandered a bit, I think he also had a small vibration but I don't recall all that well. After he did the c&t, the truck was perfect. It rode and drove like a brand new truck that was not lifted. Steering was tight and responsive, ect ect ect. I think the vague steering is normal on FJ80's. Mine has it and so did Krazytoys. I am used to it now but don't care for it much. So, the main goal with the c&t is to correct the castor without the need for any bushes, brackets or anything at all. At the same time we point the pinion at the t-case meaning the u-joints in the shaft are neutral going down the road. The c&t removes aftermarket parts form the equation meaning the suspension is basically stock in front. On top of this, on my truck I gain ground clearance. Not having aftermarket bushes or brackets also means it is easier to service or get parts for and it uses OEM stuff. If the steering tightens up how I expect it too, I am that much more stoked. It is cheap to do too, less money than buying bushes, brackets or whatever and puts the front end back to a stock configuration. It is win win in every way. Some might say, well factory welds are best and I wouldn't trust nothing but factory welds. That is nice I say, I have tested Krazytoy's welds on more than one truck (three trucks actually) and have 100% confidence in his work. And yes this means, he is helping me do the c&t!
Do I have some vibes? Not really so much. This 80 is not full time 4wd, if it was maybe I would have some more vibes. I do get some vibes at a specific speed on the HWY but right now I can not say for sure if this is due to tires/wheels or prop shafts. Since I am running an FJ60 split t-case the rear prop shaft is a bit off-set. To figure out what is causing the vibes is going to be a process of elimination. New tires & wheels all balanced up. Still have vibes, send the driveline out for a balance. Still have vibes after that perhaps a cardan shaft is the answer or I need to start looking at trans/engine mounts. The vibes I have though I could live with, they are not bad and are only at a certain speed on the HWY. It is not a wobble in the front end or a shake or any of that jazz which would drive me nuts.
Cheers