They had better be brand new gears, or at least a tooth contact pattern would need to be run before the 4.10's are removed from whatever they're in now. Getting a used set of gears back in exactly the same running relationship in the original housing is difficult- - - -if you're putting them in a different housing it's dang near impossible to do without inducing a permanent gear howl. I've got a set of Dana type 60 3.78 gears I swapped from a Ford 3/4 ton housing into a GMC rear axle in my 59 Burb. I set it up as close to right as possible, and I still look over my shoulder for that fire truck siren that's following me around at times!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!