There are no new 4.10 gears available for the original rear axle- - - -the supply of OEM gears dried up decades ago from us dirt track racers grabbing every set we could find. A late 1960's through mid-70's 3/4 ton Suburban with an automatic transmission, and a few of the pickups with automatics ran the 4.10's that people are searching for now, and those rear ends are very scarce. A better choice of a complete 8 bolt rear axle assembly with better gear ratio selections available would be a Dana Type 60 from a 3/4 ton GMC, Ford, or Dodge box van. The pickup rear ends are a bit too wide to fit your truck without fender modifications.
Jerry
