Your assumptions on the column and bracket angles are correct Bill. I see no reason a lower cover couldn't be fabbed (or modified) to match your column angle. The lower cover does nothing to retain the columns in any of the tri-fives. The column itself bolts to the lower protion of the dash and the cover simply bolts to the bottom of the column via a welded on bracket and one screw.
The dashes on these cars are welded in so finding one "loose" will be a trick. Go here:
TriFive.com, 1955 Chevy 1956 chevy 1957 Chevy Forum , Talk about your 55 chevy 56 chevy 57 chevy - Belair , 210, 150 sedans , Nomads and Trucks, Research, Free Tech Advice
There is a 55 being parted out right now and you can ask if anyone has a loose dash.
Mark