RMD withdrawals for mixed account types (403(b) and a Trad IRA)

I've seen this thread in the sub and the below page from the IRS, but I'm a little unsure how to interpret the situation of a 403(b) and an IRA. My mother and father both had 403(b)s and my mom passed, so my dad now has her 403(b) balance in a trad. IRA. Is it possible to calculate the amount of the RMD for each each account, but then withdraw the whole amount out of the IRA? The IRS table row called "How should I take my RMDs if I have multiple accounts?" assumes either "multiple IRAs" or "multiple 403(b)s" but doesn't give any advice for a mixture of account types.

https://www.irs.gov/retirement-plans/rmd-comparison-chart-iras-vs-defined-contribution-plans