69 Dart Bucket Seat Questions

The trans tunnel is NOT centered in the car. It is offset to the right about 2".
I put buckets in my 64 Valiant and had the same concern. I just finished reupholstering my rear seat and the floor hump cutout in the seat bottom is not symmetrical either. The offset hump carries right through to under the rear seat. And you probably know the engine is offset to the right also.

No to your second part. I've never had a Mopar do that. Look to see if you can somehow reverse the linkage under the passenger seat.