Let me go over what I get is the situation-->
(a) you have a home in India with a mortgage through a local lender.
(b) this lender has provided you document substantiating mortgage interest collected for the Indian Tax years 2017/2018 and 2018/2019.
(c) For claiming the mortgage interest on your 2018 US return, you need to allocate your interest payments to 2018 calendar from the Indian tax year.
As I see it you have two options in achieving this --- your option (2) above will substantially achieve this with some error but probably can stand a challenge
OR
you can get back to your records of the monthly EMI payments and convert these to US $ at the then exchange rate. I say this because Indian lenders use ( as I understand ) a variable rate that can/do change from month to month and therefore can be easily computed using an excel spread sheet ( but not using excel functions because these assume a fixed interest rate ). Also in such a case change in exchange rate can be easily accommodated., as long as you know the outstanding Principle amount. This is much more accurate method but obviously takes more effort.
You definitely cannot use your Option(1).
Namaste ji
