Currie may not sell one that fits but I have seen a Dana 60 under a 1961 Chevy Impala belonging to Mike Castellano the famous Pro Comp driver. The rear end is big, but still not as large as a stock 1957-'64 Pontiac-Olds rear that has a 9-3/4 inch ring gear and 31 spline axles. That was stock in every car made by GM not just under hot rods like Ford and Chevy did it.
Rear ends (and transmissions for that matter) are rated by torque. Basically you lock up the rear end and put power into it until something breaks. GM went to new nomaclature that tells you the relative strength of a part (In the case of transmissions they compared it to an Alison out of a school bus). So the TH400 became the 3L80 and the TH350 became a 3L45, while it also tells you how strong a 6L95e transmission used behind an LS-7 Corvette engine must be.
The 30 spline axle Dana 60 was rated, by Dana-Spicer, at 1,500 ft-lb continuous input, 5,500 ft-lb max peak input. The 35 spline units are rated to 2,400 ft-lb, which is limited by the strength of the 9.75" ring gear.
The Pontiac-Olds rears are nearly as strong (the housing is the weakest link with the tubes bending under load). It is a company that doesn't want to be bother by a special order that would probably have gotten the salesman fired had his boss learned he is telling potential customers to go away.