Greg is correct, the M8's have the same cab signals as the M7, but also are equipped with Amtraks ACSES or whatever the initials are. From the pictures I have seen of the cabs, they are identical to the M7's except for the headlight switch being lowered, the addition to the Amtrak cabs, and the changover switch for AC/DC.
Also, all cars will have to run thru the test period.