What are the different casting numbers on a 68, 69, and 70 B-body Dana rear end with 3:54 gears vs 4:10 gears? I always thought it was the tag on the rear that told you the gear ratio, but I am not sure.

There is a chart somewhere here in the tech archives, if you have a dana now, post the BOM number located on the passenger side axle tube rearward facing.

More info here: https://board.moparts.org/ubbthreads/showflat.php?Number=7685361

Any rear end that old may well have had the gears changed at some point. The ratio may be the same as original or some other ratio. You would need to count gear teeth, dividing ring and pinion count to determine ratio, or look for stamping on the od of the ring gear to verify ratio.

You can get a rough idea by rotating the tire off the ground and counting driveshaft revolutions per single complete revolution of the tire.

The BOM number stamped on the housing will give you information from the date of manufacture, etc.

Thanks for the information. Very helpful.
I have a b-body dana 60 that I am going to sell and did not want to misrepresent the item. Will see if I can find the BOM and assembly date numbers first.

easy to just turn the axle and count the yoke turns.Its not exact but real close.Example 3.91 the axle will turn almost 1 turn to 4 turns of the yoke.Its easy to pull the cover on a dana and count the teeth or look at the ring gear for ratio.Rocky