duster rear end

Can anyone tell me the length of the rear end housing for a 70 duster. I have a 7 1/4 inch rear end and I am putting an 8 3/4 in . I have 2 that I can look at. I need the total length before the drums. Thanks

From wheel mount to wheel mount 57 1/8". flange to flange just the housing is 51 1/2" to 51 5/8"