If it were me, I'd staple a copy of the trust's PTE and 740NP-WH to the grantor letter and let the grantor's preparer figure it out. With my luck, the grantor's preparer would be me, too - in which case no one is ever gonna look at that grantor letter anyhow, and I might be tempted to save the staple.

Also, that Federal 1041 is already delinquent. The current extended due date is 9/30. You've got until 11/30 (or maybe 11/29) before there's a late filing penalty for a purely grantor trust, though.