Grigg, one reason the 4.10 Eaton gears are so scarce is the fact that they were almost exclusively used in 3/4 ton trucks with automatic transmissions- - -the "Camper Special" pickup, and some Suburbans with 3/4 ton suspension. Another reason is that us 1/4 mile dirt track racers scoured the wrecking yards in the late 1970's looking for those rear ends to run in our race cars. The combination or a 1.88:1 Muncie 4 speed 2nd. gear and a 4.10 Eaton rear end was just right for running on a quarter mile round track.
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!