It's unlikely that splitting the Form 1099-R is the correct thing to do. As I understand it, the entire 401(k) was rolled over to a traditional IRA and you later did a Roth conversion of $50,000 from the traditional IRA.
What is the code in box 7 of the Form 1099-R from the 401(k)?
Does this form show a nonzero value in box 2a?
Does this form show your after-tax basis in box 5?
