8 1/4 F Body rear end fit in an a body?

It will fit under your car. I have f body 8 1/4 under my duster.
As Goldduster360 replied spring perches are difirent and those are difirent shape. Y also need 3" U bolts for that rear. Drum to drum is about 1,2" wider each side. Oh and you have to modify 7 1/4 rear shock plates so those U bolts will fit.