The vents on the power door, the latch being a thumb latch rather than a hook-bail latch and the presence of the slipfitter bolts sticking out of the top. The photocontrol is also moved back while the A2 has no vents on the power module and there is no bolts on the top and the photocontrol is moved forward.
@ Burrito : The M400A2 does indeed have vents on the powerdoor ! I have 2 of them (1986 & 1990 ) The A2 also has a street side mounted socket , A latch on the powerdoor along with the holdown screw and the slipfitter is different . Plus , the late A2's don't have the "body line" on the upper housing that the M-400 has had since the beginning .
