There are a bunch of different kits that can be used to put a rack into an E-body car. Most of the the kits are designed for drag racing, but there are a couple that are aimed more towards the GT crowd. They are all fairly expensive ($3000 or so).

You didn't say what you were trying to accomplish so it is hard to help much. If you just want to make the steering a little better then get your box rebuilt by the guys at Firm Feel. There is a ton of stuff that can be done to tighten up the stock steering system. 11/16 tie rod ends, bracing the K-frame around the steering box, etc.

I covered this topic in my B-body book so maybe start there. There is also information in the old Mopar Chassis book as well as various out of print Mopar suspension books.