$476 to assemble an 8 3/4 diff

You need a press, possibly a bearing separator, spanner tool, inch/lbs and ft-lbs tq. wrench, a large vice, pinion depth checking fixture and the other mentiined tools to ensure a successful mission. Too much work involved to do a job like this twice.

Ps it if it was a Dana 60 you would need a case spreader too.

Doing a job like this without the tools mentioned above is possible but you are rolling dice on the outcome.
What is this pinion depth checking fixture that you mention?