01 Tundra differential confusion

So I’ve recently had my truck in the shop and my mechanic made some comments about how poor shape my dif was in, so I began looking online for replacement covers but come to find out by looking at my dif that it has no back cover? Anyone have any help or explanation for me about where I should go from here?
Attached are pictures of front and back of rear dif

 

How's the rest of the undercarriage look?

 

Does it have a hole in it?? Looks like it should just buff out....

 

Take it to a shop and have the old cover cut off and a new one welded on.

http://www.barnes4wd.com/Toyota-T10...ndra-Heavy-Duty-Differential-Cover_p_359.html

 

ive taken ad cleaned them up with a wire wheel and gabbed a large amount of jb weld and coated the whole thing with that sanded it primed and painted it
held up ever since

 

Frame was replaced 3 years ago as well as all suspension pieces are being swapped out, so the only rough looking piece left will be the rear and front axle, I can paint the axle but just wanted to strengthen up/replace dif cover!

 

This is the right way to go here. I guess it depends on what the rest of the axle housing condition is.