Well....hmmm. '57-'59 Fords are not exactly common around here and nearly everyone recognizes the value of a 9" Ford rear - even if it's really an 8". Add in the fact that 8.8 parts are still cheap right now.....I can have my pick of 8.8's and a limited slip version goes for around $75 here........plus it's more efficient than a 9"....it makes an 8.8 look better and better.
The problem is finding one to fit. I was hoping someone had already spent the time scouring the junkyards and measuring them, so I wouldn't have too. ;o) Okay, so I'm lazy! ;o)
A 9" is going to be the second choice.