I wouldnt buy used gears but thats just me....Summit racing sells Ford Motorsport 4.10's for the 8.8. They run about $170. Those are the ones I would get. Being a Ford guy, I can tell you that they know what they're doing when it comes to this stuff.
As far as the locker....If you get a powertrax (lock-rite or no-slip) it just replaces the spiders. If you get an ARB, Ox, or Detroit it replaces EVERYTHING including the carrier.
[url="http://community.webshots.com/album/37357975IlmeHK"]'92 YJ Islander[/url], 4.0, 5-speed. 1" Daystar Body Lift, 31x10.50 Goodyear MT/R's, CJ Style (87-91) Roll Bar, ARB Safari Snorkel, K&N Panel Filter, Dynomax SuperTurbo Catback. Still hunting for TJ Sahara flares!!!
[url="http://community.webshots.com/album/37557247daBfyQ"]'87 Mustang T-Top GT[/url], Maximum Motorsports: Rear LCA's, 4-point K-Member brace, & Std Length Subframe Connectors, FRPP 'C' Springs, Mac Pro-Chamber, Chrome BBK equal length shorties, B&M Ripper w/ leather cobra knob.