I have a Canon IIb which has no flash synch of any type. The full gate speed on the b is 1/20 sec, I think the IIf has a full gate speed of 1/25? No matter, the full gate speed would be your max X synch speed. Typically when the first curtain is fully open, the X contacts close. It might (should?) be a simple matter to retime the existing contacts and use the existing bar as a connection by making a connector to slide onto the bar. I would not, at this point in time, modify one of these cameras in any way. Retiming the existing contacts and using the existing connection would be a way to get X synch without making any permanent changes.