The two appear to be generally pin compatible, with a few exceptions:

One exception is that the M7050 has an "on/off line" input on pin BU1 that must 
be high when the reader is on line.  

Another exception is that the M7050 detects an "out of tape" condition if no 
character appears within 7 milliseconds of an enable.  This output is also 
forced for the "off line" condition, and is presented on BL2.

The M7050 also presents "inhibit_strobe\" at pin BT2.  This signal is basically 
a delayed version of FEED_HOLE.

The M7050 has an additional input on BC1, which when grounded will disable driving 
the input bus during RRB.

The M7050 has an additional test point brought out on pin AC1, which carries the 
enable for the reader data latches.

The M705 initializes the input buffer to 0000 on INITIALIZE.  The M7050 will leave
the prior contents.

The M705 loads FEED_HOLE with two TTL loads; the M7050 uses a pair of MPS6531 in 
a darlington arrangement that adds a small delay and has an AC impedence of 330 
ohms and a DC impedance of about 5K.