That's a Rubicon Express SYE "Hack-n-Tap" flange on the left and a CV jointed driveshaft on the right. The hack-n-tap shortens the output shaft on the t-case, allowing for a longer driveshaft and CV joint, reducing operating angles slightly.
That's the stock rear driveshaft, front toward the left. That short piece with the bellows slides over the output shaft. As you can see, the stock driveshaft has no room to extend/collapse. Instead, differences in operating length during suspension movement are taken up as the driveshaft slides over the output shaft on the t-case. With taller lifts, there isn't much room available on the output shaft for that kind of movement, and applying torque when the splined surface is barely covered can lead to broken parts.
T-case drop - look at the transfer case crossmember. If it's mounted flush to the framerail above, you don't have a t-case drop. The drops usually consist of four 1" tall pieces of round aluminum stock with a centered hole drilled through them. Longer bolts are used to hold the t-case crossmember to the framerail, through those pieces.
If you have an SYE and CV driveshaft, you really shouldn't need a t-case drop.
