The (Zinsco?) bus bars have arc marks. Can you file these down to bare metal?
No, cleaning the bus is not acceptable. Never seen a replacement bus for Zinsco panels. The existing breakers reportedly have 1300 series aluminum alloy that is not suited for non-bolted connections like the connections in the old breakers.  A replacement bus to be safe would need to also have replacement breakers, that start at $30 for a single pole 20A breaker, and a 2p30 is $65. The math starts to get rough, and then would be worried you might not end up with a quality install anyway. 

The ground in a subpanel should be connected to the ground in the panel feeding it, the neutral in the sub should be isolated from the ground in the subpanel.