I have searched the site for the differential ratio that came on a 71 240 with an automatic transmission. I am planning to remove the auto and install a 5 speed and need to know if should also grab the rear end from the donor.

Thanks

As far as I know all the automatic equipped cars in the US came with a 3.54:1 rear gear. A bit better than the 3.36 manual transmission ratio but not as good as a 3.90 or 4.11 would be with a 5 speed.