SJ diffs don't fit the 410 axles you would need to source some LJ80 diffs, these drop straight in with the third member and reduce the overall gearing a fair bit. I forget how much exactly, I'll try and remember to look it up later.
Edit:
The FSM gives the stock 410 diff ratio as 4.111:1
The LJ80 is quoted on the web as 4.556:1