Help with Rear Brakes

I have a 79 camaro and one of the springs broke in the driver's side rear brake drum. It is the one in the middle of the drum on the right side (toward rear of the car). I went to get a replacement and the kit specified for a 79 does not match my brakes. I assume this means my rear axle is not from this car. It is a 10 bolt and the only digits I can read of the code on the passenger side tube says PAC 615. I can't find a casting code. I am trying to identify my axle to see what year it came from. Please help, this is stopping me form driving this car.