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IOW, can I R&R my '66 noncollapsing column with a collapsing column from a '68?
I hate to say this but sometimes you need to bite the bullet and get the part, once you have it you will see if it'll work or what it'll take to make it work.
Particulars to look at:
Steering gear coupling
Floor mounting plate(s)
Dash mounting plate
Shift bell-crank (lower lever), bends, direction...
You will probably need to use the entire column assembly as the housing, shift tube and steering shaft are all part of the collapsing system as is the dash mounting bracket.
Peruse photos. At least in A-bodies I know the brake pedal changed at some point between 1965 and 1974 to go around the opposite side of the steering column, which might have been for the change to a thicker collapsible column. If you are going for the collapsible feature, you might want to disassemble and insure the sliding rod will collapse since I think some are rusted tight.
The 64-66 A-Body is a different animal than the 67-76 you could probably swap within the two groups but not between them.
I feel a 67/68 should work in a 66 (C-Bodies)
There are no slip joints in the collapsible column, at least not that can be inspected by slipping. The sections are fused together with plastic plugs that sheer on impact, only the outer housing actually crushes.
This is the shift tube on a 69, you can see the sheer pins in the upper right corner of the picture on the upper tube.