Grantor Letters are not uncommonly used in place of a more formal "Schedule K-1" for a trust, but you can use the Schedule K-1 for Form 1041 to help guide you as to where to sprinkle those number into your own income tax return.
Go look at the Schedule K-1 for a Form 1041
https://www.irs.gov/pub/irs-pdf/f1041sk1.pdf
and scroll down to the last page there. Those are the instructions to the recipient of the Schedule as to where information shown on Schedule K-1 goes in their own income tax returns. You'll see that Box 4a amounts go on "Schedule D, line 12."
Back in the day when income tax returns were filled out by hand, that was an easy instruction to follow. But unless you are using a desktop product that allows you direct access to the Forms/Schedules/Worksheets it can be difficult to know how to get that number on the "right" spot in the "right" form.
If you want to follow the IRS's direction explicitly then go over to the Schedule K-1 interview, be sure to select the Schedule K-1 for Form 1041, (Estates and Trusts), and enter stuff that way. Don't worry in the slightest that you have to make some things up because nothing you make up - name, address, Federal ID number, etc - shows up in your income tax return.
Tom Young
