if i look on ebay to buy a set of 3.73 gears for my 95 thunderbird with an 8.8 rear end is there anything i need to know or look for? is it wise to buy a set of used gears? also are they all the same if it says 3.73 for an 8.8 ford. there was one from the front end of a 2006 f-150. i wasn't sure if it would work. also one from a 2004 ford explorer. if i'm just buying the ring and pinion can i buy any of these and have them installed into the mark VIII carrier i have?