[Cal Metal]

Goober:

The 390 FE motor originally came with a 28 spline, as opposed to a 31 spline big out tail. It also used the 1-1/16 input as opposed to the 1-3/8 inch style. The 390 could be had with either the wide or close ratio gear sets; the 427/428/429 came only with close ratio sets. David Kee does make a wide ratio big in/big out gear set which is really great for guys with 3:36 and 3:55 rear end ratios.