First of all, I don't have any GM interchange information on turn signal levers. However, I do have information (hopefully correct information) on 1978, 79, and later Corvette levers.
The 1978 through 1982 Corvette T&T columns had a pivot inside the steering column head where the turn signal lever just "plugged" into. Just a straight push or pull should facilitate installation or removal. This makes installation and removal of the lever quite easy. The only thing that makes it somewhat difficult is if the lever has a cruise controls and wiring attached to it. I think that the wiring has to be "fished" down the column if you change the lever. All of these levers (1978-82) should interchange and just plug-in to the dimmer pivot.
Now it starts to get a bit more confusing. The angle of the pivot inside the column changed sometime during the 1979 model year. It started out at a shallow 21 degree angle. This required that the turn signal lever (with cruise) to have a 30 degree bend in it. This compensated for the shallow pivot angle and brought the end of the lever (with the cruise button) close to the steering wheel rim. BTW, the turn signal lever without cruise was straight.
Sometime during the 1979 model year the dimmer pivot was changed to a steeper 46 degree angle. This brought the end of the turn signal lever close to the steering wheel rim without having a 30 degree bend.
Now, I don't know what type column that you have (I assume that you have a T&T since nearly all Corvette columns were T&Ts by 1979). Also I don't know if you have cruise control or not.
By just looking straight down on the column, you should be able to tell if the turn signal lever is coming out of the column head at a shallow 21 degree angle compared to 46 degrees. Knowing what angle may give you some alternatives. For instance if you don't have cruise and you have the straight lever. You might find if helpful to use a bent lever with cruise and just cut the cruise wires off. If you have cruise, it might be helpful to change to a straight lever or change to a bent lever depending upon your situation.
The following comes from my T&T Strg Column Disassembly & Repair Paper #3 dated 19JL2009.
---------------------------------
Dimmer Pivots & Turn Signal Levers
The 78 to 79 - The turn signal lever w/cruise (GM 25030522, ZIP SC-337 or Doc Rebuild #2897116) had a 30 degree bend in it because the dimmer pivot had the lever mounting hole that was at a shallow angle (21 degrees) and the lever needs to bend toward the steering wheel rim such that the driver can easily reach the cruise button.
The 78-82 T&T turn signal lever w/o cruise was GM 14009242, ZIP SC-333 or Doc Rebuild #2897118. It was a straight lever.
The next change occurred late in the 1979 model year. The angle of the turn signal lever mounting hole in the dimmer pivot was changed to 46 degrees. The turn signal lever now was pointed more directly at the steering wheel and the turn signal lever was straight. Zip Products lists a 79L-82 Turn Signal Arm Pivot Assembly SC-756. This should be the pivot that works with straight turn signal levers.
Here are the straight T&T levers that I think work with the 46 degree pivot:
GM 25030492, Zip Products 79L-80 Turn Signal Lever w/tele & w/o cruise
SC-332.
1981-82 Turn Signal Lever w/cruise (Resume Switch on side of lever) Doc Rebuild 289119.
--------------------------
The entire series of Disassembly & Repair Papers can be found at
www.corvettefaq.com
Click on Jim Shea's Steering Papers
Click on Corvette Steering Papers
Scroll down to the Tilt & Telescoping 69-82 Section
Jim
PS Upon reading your original Post, I don't believe that any of the options that I sight will necessarily shift the lever up away from your leg. Sorry.