It doesn't matter, the firing order for all straight sixes is the same. For example, it is said that the firing order for a Ford V8 is 15426378 and the firing order for a Chev V8 is 18436572 They look different, but because Ford and Chev number the cylinders differently, they are actually the same.
The cylinders run 1-2-3-4-5-6 front to back. The firing order is 1=5-3-6-2-4 A 62 full size Chevrolet should have a 230 rather than a 235 though. The distributor will be more towards the front of the block rather than in the middle like a 235.