K member question

Not sure what your after, "K" member will bolt in an "A" body from 1967 to 1972 and up.
I'm not sure but a Demon could have come with a 6 cyl, They make motor m "K" frame ount conversion kits where you can put a V-8 in a 6 cylinder "K" frame. Or you could find a V-8 "K" from another car to bolt in it.
Somewhere around 1972 and up they used a spool type motor mount rather than a biscuit type in the previous years, that would also bolt into a Demon.

If your after say, a numbers matching 340 Demon and the washer is not on the "K" frame like in the above post than it might not be correct for the car.