I am submitting a determination letter request under Cycle C for an S Corp ESOP. What there a deadline by which the plan had to be amended for the final nondiscrimination regulations under 409(p)? If so, do you have a cite?

This was an EGTRRA provision so it would have the same required date as any other EGTRRA changes UNLESS you were not an S corporation at that time. If your S election was later than that, the amendments should have been in place by the end of your first S year. I don't know that it is entirely clear whether these amendments would be covered by the 401(b) remedial amendment rules because they are not qualification issues for the plan, they merely go to the plan's status as an ESOP. But, I would like to here from other ESOP gurus to see if they agree with that conclusion.