Subject: Re: Partial IRA to Roth Rollover
Well, I just came across this:

https://www.irs.gov/pub/irs-pd...

Page 21 top right:
Tax treatment of a rollover from a traditional IRA to an eligible retirement plan other than an IRA.

Ordinarily, when you have basis in your IRAs, any distribution is considered to include both nontaxable and taxable amounts. Without a special rule, the nontaxable portion of such a distribution couldn’t be rolled over. However, a special rule treats a distribution you roll over into an eligible retirement plan as including only otherwise taxable amounts if the amount you either leave in your IRAs or don’t roll over is at least equal to your basis. The effect of this special rule is to make the amount in your traditional IRAs that you can roll over to an eligible retirement plan as large as possible.

I read this as saying I can roll over the pre-tax part of the traditional IRA into my eligible retirement plan (401k), leaving only the after-tax basis, which can then be rolled over to a Roth with no tax due. Does that seem right?