Don't know if it helps but I went out and measured the shackle proportions.
I will do my best to describe the the measurements I took.

There is the bottom "sleeve" that houses a bolt the goes through the shackle sleeve and attaches the leaf springs to the shackle. I'll call that the "B sleeve". I measured the outside diameter of this sleeve

The sleeve above that one also houses a a bolt through the shackle sleeve and attaches to the frame rails through a a bracket on the frame. I will call this one "A sleeve" I measured the outside diameter of this sleeve.

I also measured each sleeves "Shackle width". If you visualize the shackle it is two pieces of steel mated with the sleeves in the middle and spanning the distance between either piece of steel.
By shackle width I measured this at both ends past/after the sleeves.

I also measured the frame to shackle mount/bracket width. This is the two pieces of steel that come down from the frame and attach to Sleeve A.

Sleeve A= .9 of an inch
Sleeve A shackle width= 3.9 inches
Sleeve B= 1.12 inches*
Sleeve B shackle width= 3.12 inches
Frame to Shackle mount/bracket=1.9" inches in width

Hope this helps, Gonna email this to the ARB tech email and see what they say comes close to this or what would be a better measurement to help narrow down to the closest grease-able shackle option while still functioning with the ARB/OME parts:
OMECS022R- Rear leafs for Gen1 SWB
OMEU54- U-bolts
OMESB8- bushings