I personally didn't have any ATP questions on my ATP+type Captain upgrade. It was with a company check airman and majority of it was systems and then the company Ops Specs and that was it. Thankfully the oral was 45 minutes. Its worth it to be over prepared for an oral and thankfully not hard to do just hard to find the time to do it.

I'm in my 9th year and I don't think I've ever cracked open Part 121 FARs outside of the ATP written. Its about what your company is or is not FAA approved to do.