Old Doc, the B29

Magnificent.

Here is the story of the two WASPs who ferried early B-29's across New Mexico for a few days. Many experienced combat pilots considered the new Superforts unsafe because of a well-known and documented problem of engine fires. These men had risked their lives over Europe, but were reluctant to take needless risks in a new, hastily tested aircraft that had a habit of spontaneous combustion.

Col. Paul Tibbets recruited a couple of WASPs to check out in the B-29, but didn't mention the engine fires to them and had them skip pre-flight runups that often resulted in fires. Then he had them fly short ferry missions in lightly loaded bombers that (presumably) didn't require anywhere near full power for takeoff.

https://www.pbs.org/wgbh/americanexperience/features/flygirls-wasp-and-b-29/

I don't think the run-ups referred to in the article are mag checks. From the context it sounds like run-ups of the four engines one-at-a-time to check things like oil pressure and temp, cylinder head temps, and manifold pressure.

These were new engines that were temperamental thoroughbreds, pushing the envelope of what was possible with pistons. I think the run-ups were intended to identify potential failures prior to finding yourself nearing takeoff speed with not enough runway remaining to stop and not enough power to fly.