However, the Centronics port is defined as a 5V interface so there could be some interface level issues. The GPIO output of the esp8266 will be fine for the logic 0 levels but the 3.3V output could be marginal for the logic 1 levels. Theoretically it claims to use TTL levels where 2.0V is sufficient, however, the picture seems to show that HC logic is used which might need a bit more. There is a very good chance it would work and if this is just a one-off then it may be worth trying. Otherwise you will need a level shifter. There is one input signal fed back from the interface (/busy). This will be at 5V so should not be directly connected to a GPIO on the esp8266. You could simply put it through a 2 resistor divider. E,g, /busy to 2.2k resistor, 3.3k to GND and the junction to be fed into the esp8266 GPIO to monitor /busy.
On the bitmap you seem to be using the function on 4-49. You are sending the command and sizes but the bit map data does not seem to be right. First it starts with a space rather than a number, second it does not seem to have the right amount of data for the size you have defined. Third you need to send the data as binary values.
If you look at the diagram on 4-56 you can see that x=64, 8=96 corresponds to a 512 x 768 bit map image and needs 96 bytes to define each column and 512 columns. It therefore needs 49152 bytes of data. (Diagram seems to have a spurious 9 in the final column labels)