1C main case is out of an early 61-62 car. Probably out of a Nova, Impala, Corvette with wide ratio, depending on how many splines are on the input shaft and yoke. I think there were a couple of first gears available (2.20 or 2.54). Super T-10 would be more valuable.
Hard to put a number on it without knowing original application, condition, and any internal upgrades (nickel inputs, etc.). Maybe $350-$550.
Some people prefer cast iron to aluminum as well. There is a buyer for everything, though
