lots of little questions pertainting to an 8 3/4 swap

ive got an a body 8 3/4 im going to put into my 73. i bought moser BBP axles for it. ive heard something about removing the thrust blocks to put new axles in? whats the deal with this could anyone explain? i dont belive it said anything like that in the directions that came with the axles. what do the thrust blocks even look like?

Do i need a different driveshaft? im going from a 8 1/4 to 8 3/4

i have another 8 3/4 with 11 inch break backing plates. my dads friend said they might stick out more. is this true?