There may be one but you might want to read this.
http://www.popularhotrodding.com/tec...all/index.html
I also found this on a Z28 board.
http://www.nastyz28.com/forum/showthread.php?t=78970 That thread is about three years old and it is the latest thing on the subject on Google that I can find. The only conversions that I found reference to would be pretty much drag race only with somewhat light weight racks that I wouldn't want on a street driven truck.
You can do variations of the search that I did, Second generation Camaro/Firebird Rack and Pinion steering and may find some more results that I didn't find. From what I read on that Z thread the general thinking was that going to a rack caused more issues than it fixed.
Personally I think a quick ratio box for a late 70's Trans Am would be the way I would go if my original box was shot. Sometimes the "look what I got" factor isn't as viable as what really works that was designed for the application.