To The OP, Trust me when I say swap the engine and trans both or not at all.
unfortunately, i may have to agree with this.
looking through my myriad of FSMs, the 1960 plymouth manual shows an 8 bolt crank flange on the 361.
with that being said, i don't know if if the bolt circle is the same diameter as the later 6 bolt 383. if it is, it may be possible to machine up an adapter to make the crank flange the same length as the 361, then modify the flex plate from an 8 bolt to a 6 bolt by slotting a couple of holes.
however, i would have to see both cranks and be able to precisely measure the flanges and the bolt patterns to be even remotely certain this may be feasible.
