Our end of draw HELOCS will still be an adjustable rate according to the WSJ on the last day of each month, which means that the payment can change monthly based on the remaining balance even though the rate may not change. Does anyone do these now? If so how are you complying with the requirement to send an ARM notice at least 60 days prior to the change when you don't know what prime will be that far in advance?

You don't send ARM notices on HELOCs. They remain open-end credits and are subject to the periodic statement disclosure requirements.

Our core processor is telling us that once they are at end of draw and go into P&I payments that the notice is required because the P&I can change monthly (depending on if the borrower pays extra, 30 vs 31 days in the month, etc).

Your core processor is wrong, unless you are refinancing the HELOC into a closed-end loan, they remain subject to all of the open-end rules. What they are probably trying to tell you is that they don't have the ability to process a HELOC that has reached the repayment only phase and they are giving you some cockamainy story- I know of at least one core loan system that can't..