A little further down the rabbit hole...
Looked at the T-bars, ends are stamped 456R/092 (R) and 457L/231 (L).
They measure .850" about midway.
Everything looks basically new or rebuilt.
Restoration has about 4,000 miles on it, car had under 69K on odometer before that.
Those 456/457 #s don't show up on the broadcast sheet ("779 left" / "778 right"), nor in my MP chassis book.
I suppose it could have drag race bars in it (FSM spec is .88"): though that doesn't match the rest of the restoration, the car did make a few passes in its past and has Calvert shocks in it.
(Possibly misleading comparison/reference: my SB Duster has even smaller bars, been in there almost 50 years, no sagging, but it's 3000 lbs & has never seen street use.)

I'd like to sort this out before the wheel alignment, will also try R/L tire swap to check for "radial pull".