I can tell you that what you are trying to do very difficult. Not the steering column, but the rack and pinion on a straight axle. The problem you will run into is the axles up and down movement, plus being in a arc. This creates a hugh problem for the steering column to stay connected to the rack while compressing and extending trying to keep up with the axle.
You will need a very elaborate flex joint that will not pull the pinion out of the rack. Pinions are not made for this type mounting, there is a reason racks are mounted to the solid frames with the ends being flex able.
Steering columns are easily cut and shortened using standard hardware bearings. Getting the shaft into ' D " shape is easy enough with a grinder and a file.
Jump over to the Jalopy Journal web site, this has come up many times and you will find plenty of reasons to continue or quit now.
Here is just a taste of what has been discussed,
http://www.jalopyjournal.com/forum/showthread.php?t=844765&highlight=rack+pinionwww.Jalopyjournal.comJoe