All growth in a traditional IRA is pre-tax.
The main thing that you need to be careful of is that the value in the traditional IRA doesn't drop below the basis amount after the pre-tax portion is moved out, otherwise some of what was assumed to be pre-tax when moved to the qualified retirement plan transforms into basis that was impermissible to have rolled over. It probably makes sense to put an amount equal to the basis into a stable-value fund before rolling the rest over to the qualified retirement plan, then convert the stable-value fund to Roth, ensuring that you can convert to Roth no less than the amount of your basis in nondeductible traditional IRA contributions.
Doing the rollover to the qualified retirement plan first ensures that that rollover can be completed before you commit to the irrevocable Roth conversion.
