Not the greatest but
The rear edge of the seat does not look parallel to the trap door. There was another picture that hinted at the same non-parallel mounting, showing the RH side is forward. Maybe the LH side needs to go forward to straighten the seat out. On the two current Fastbacks I have (a 65 and a 66), neither seats fit well in the front with the seat down.
Jim
It took a while (I have a lot of pictures to flip thru), but here's a sketch I made of the bracket's location for a friend that "adapted" a 66 fixed rear section to be used in his 65 Fastback. Both sides need to be the same.