I have looked through various Chevrolet Chassis Service Manuals as well as some Saginaw Steering service liturature. Not one shows an accurate blowup of a 1978 Corvette T&T steering column. However,
I can sort of combine the best of two Service Manual blowups that will come close.
The best single blowup is entitled: Corvette C3 Tilt & Telescoping Steering Column Blowup (1969-76 Shown)
It really is a C3 Vette T&T column before 1977.
It shows the telescoping steering shaft (parts 40, 41, 43)
The mast jacket #63 does look like the Corvette part.
However, it includes quite a few parts that were not needed on a T&T steering column like your 1978 such as: #66, #60, #58, #56, #54, #53 and #11.
There is a generic tilt column blowup that exhibits the additional features that were introduced on the 1977 and later Corvette columns. Those features; the key release and the headlight dimmer, added some parts
such as #44, #45, #46, #47. #62, #63, #64, #86, #87
and deleted parts from a Corvette T &T column as listed above.
Maybe someday I will get ambitious enough to actually try to cut and paste the above two blowups into one correct 1977-82 T&T column.