I would say quite
I would say quite emphatically: get the frame replaced.
If your live in the Midwest salt belt, it is only a matter of time before a Dana-made Tacoma frame rots out. If the frame still looks good on a Michigan truck, it is probably a fluke. Maybe the previous owner only used the truck in nice weather when road chemicals were not in use.
My Tacoma started to show serious rot in less than one Cleveland, Ohio winter.
Dana is capable of making parts that do not rot. I have a 1963 Studebaker with a Dana axle and differential that still looks fine after 54 years. I presume that Dana made the frames to Toyota's specification, and the spec. was insufficient for northern climate. I find it puzzling that corrective action was not taken sooner - Toyota has frame corrosion problems going back to the 1990s.
At any rate, the free frame replacement is the next best thing to getting a free new truck. Jump on it while you can.