Strangest thing found in your A body???
With experiance with these spiders (Bit once). Yes it's a Black Widow we get them the size of a quarter were I live. I hope you killed that sucker and looked for more. We have them so bad that when I get a new project I put it in he garage and set off atleast 4 bug-bombswhich kills the insects.
Anyway a 73 Duster 340 I bought once, when checking it out I found a breast pump and Zig Zag papers,Roaches,and pot seeds then found that the previous owner had made a fire in the spare tire well (God takes care of fools) The car was a 4spd car and led a hard life, The crossmember had 2 bolts ripping thru the subframe, found the car had been pieced together. it was completly cut in half behind the front seat and had another back half installed. Found extra bolts in the oil pan,Exhaust pipe had coors cans and clamps fixing leaks.