The center section will work from up through a 1972 and many of these later ones had 3.73 rears which is a huge step up from the 4.56 factory gears. Someone else can chime in as I've heard that there were even shallower gears than 3.73's offered behind big block automatics.
3/4 T High Speed Pumpkins Yes ~ go to junkyards & look for P & G 30 series vans with V-8 & automatic trannies, they'll almost always have the 3.73 gears . Count the bolts & match , then drop it out carefully as the dirt can ruin it , count the axle splines too at this point , _before_ you have $pent your $ . Don't be disuaded by that rusted out bashed in filthy ice cream truck ~ it prolly has exactly what you want .