These have been some good suggestions. I'll try tilting down the rear gangs on the disk this weekend and see how it goes. If I remember correctly they never wanted to dig very well when tilted back until the whole disk was lowered to the point the front engaged also. I need to check but I may be able to reduce the offset of the front gangs while keeping the back offset. This may solve that problem and still pull dirt to the middle.
I have a couple smaller old farm disks laying around I might play with. Trying to add longer braces to an old 3pt disk to look very similar to that terrace plow, but time has been a limiting factor in completing that job.
Will post back results as soon as I can test a few of these ideas.