Hey all, i've just aquired a used TM M4 and it would appear the guy i bought it from has lost the motor adjustment plate

anywhoo, do you think a washer from crappy tire would do the trick? If someone could give me the dimentions then i might be able to bore one out if its too small. I couldn't find one separately on ASCA or anywhere else domestically.
Also, the mechbox is orignally an M16 box not an M4, what is required to rewire to the back? anything fancy other than running the wires to the rear? (planning on putting a full stock on later)
Thanks in advance.