The following technical article regarding the Rear Heavy Duty Sway Bar Installation Instructions for a Flairbird is provided by Steve Auffinger ~ Yadkin. It is used here with his permission.
First, remove the gas tank. There is no way to fit the bar in without doing so. Also remove the rear wheels. Position the bar with the links facing forward, outboard of the shocks, then slide over the top of the axle. The center hump clears the differential.
The bar goes over the top of the rear end, and is fastened through bushings, U-bolts, small sections of channels and spacer plates. It fits right over the brake lines so those don't have to be moved. (The instructions suggest otherwise.) I left these fairly loose, allowing fore-aft movement while I investigated the link attachments.
The end links attach to the frame, forward of the axle, high up in the upside-down U that goes over the axle. The attachment is a small piece of angle, with a 3/8" hole in the vertical leg for bolting through the frame, and a larger hole in the horizontal leg for the rubber link bushings. I managed to position the angle to the side of the OEM top shock brace, which is heavier gauge then the frame so it reinforces this connection. By trimming a corner of the angle I was able to get the hole position further into the heavier gauge steel. I then marked the hole with a steel punch and drilled a small pilot hole from the inboard side of the frame, through to the outboard side of the frame. Then I progressed to a 3/8" bit from the outside. Don't drill an oversize hole. The 3/8" mounting bolt then goes from the angle, through the frame with a washer and self-locking nut on the outboard side.
After loosely installing the links and ensuring everything fits, I repositioned the U-bolts and bushings 5" from the spring brackets, and made sure my installation was symmetrical. My bar ended up just about directly on top of the axle tube, while the instructions show it being significantly forward. These assemblies can probably be positioned further inboard to allow more flex in the bar, or closer to the spring seats to allow less.
I then lightly torqued the U-bolts. I didn't use a calibrated wrench but I'm guessing about 20#-ft. All of the nuts in the kit have nylon inserts to prevent backing out, so heavy torque is not required. In fact it doesn't take much bolt tension to start deflecting the channel used as a spacer.
I torqued the link bolts about the same. The nut seats on the bottom of the bolt threads, and slightly compresses all four rubber bushings. There is no spacer in the link so it is as short as possible.
Torque the frame bolts lightly, otherwise you will distort the box shape of the frame.
Re-install the gas tank and wheels and you're done.