Reply by russde

You didn’t mention it…but Don or Dan (both excellent resources) recommend flattening planes with the blades/chip breakers attached but retracted as the tension will affect the sole plate.
I just got a Craftsman #5 with a corrugated bottom that had been neglected for 30 years, and tested this. It’s true. With the plane ‘empty’ the marks I placed on the sole changed when the blade was installed.

-- Upright and taking in nourishment--must be a good day