The frame chart in the factory service manual is useless for frame damage.

The only frame spec available for your 71B-Body
is contained in a book called a Tru-way Frame book. They are printed by model year ex. 1971)

You have to by the entire book to get your page.
There is a guy who still sells these. Sometimes you can find them on ebay...

Kline's auto has these, you can find an ad for them in hemmings...

NOTE: These are the only frame specs for this car!
or any other old mopar.

don't bother with the factory service manuals or any other source... Tru-way is the only thing you should look at....

Google on Tru-way frame specs or frame books and you'll see...

Good luck...