The Oliver "pipe plows" were often converted from 4 to 6 btm, or back the other way. Back in the day, we had a pipe plow (model 4441) that was delivered new with a 4 btm base section and a 2 btm add-on. 
A few years ago when we rejuvenated our piggy-back (IH 400-IH M) we started with a  6 btm 4441 that had 4+1+1 sections. It pulls as a 4btm now.

The IH #60 or #70 pull type plows were factory built as either a 3 btm that could be reduced to 2 btm, or a 4 btm that could be made into a 3 btm, all done per the OM. If you reduce the number of btms on either plow, you end with the double channel iron backbone sticking out the back, unless you cut it off. The Oliver pipe plows had plates welded on the end of the pipe that bolted together. It was a very clean looking conversion. Again done per the OM.

You can see our present day Oliver reduced btm pipe plow in this video at the 6'40" mark. That's me plowing. The 2x JD-G hitch at the beginning of the video is our friend/neighbor Jeff Lanoue.

Tandem tractors at the HCOP