Vintage Dirt Bike Q & A

Does anyone know why the cases are in matched sets? Looking at them I don't think they could be line bored like a car, or the gaskets surfaces lapped together. The only thing I could think of was that the cylinder gasket surface was machined with them bolted together. The reason I ask is because I have a good left from one set and a good right from another set. One is a real early set because the numbers are in a line and not stacked. On a Yamaha you can buy a left or a right and they don't even use a centercase gasket. I know Honda holds as close a tolerance as Yamaha.