the diff cover will likely not clear the gas tank. you need to check full bump....do this by pulling the rear springs and pushing the axle to full suspension compression.
If you can't get here, you need to address your bumpstop extensions so you can:
I know for a fact the Riddler rear D44 will NOT clear in the rear with stock 15.75" LCAs, and stock length uppers. it does rub the gas tank, been there, done that.
Here's a Solid cover at full bump (which is lower profile than a Riddler), with 15.75" lowers and 13.75" uppers and a high clearance savvy gas tank skid:
The first problem is your 16" LCA's. You need to keep those at stock length, or actually shorten them slightly. To adjust pinion angle you need to shorten the lowers slightly while extending the lowers - basically rotating the housing about the hub center, instead of pushing it back.
the next thing you need to do is check the clearance of the track bar bracket at full bump - they can hit the fuel/emissions lines.
the next problem you'll find is the rear track bar hits the frame at the gas tank mount. the relocation bracket, or moving the axle back both create this interference.
the way I fixed these issues was with a high clearance gas tank skid, 15.75" lowers, 13.75" uppers, and a custom track bar. basically a used Rubicon Express track bar with heim end + a stock solid track bar. The stocker was heated up with an oxy-acet torch and bent to fit..and the heim end was sleeved on and welded.
all this because you can't run an adjustable track bar alone...it hits the stock bracket and prevents droop. you can't cut that lip off or you'll weaken the bracket significantly. the relocation bracket also fixes the roll center in the rear, so its beneficial.
now that thats explained...you want to use a diff cover thats lowest profile. the stock diff cover is the lowest profile. i'd suggest a Barnett/T&J diff cover, or a bolt on skid like Warn or Rugged Ridge. You can also pull a 3/16" thick front D44 cover off any late 1970s Chevy, Dodge or Ford truck.