Glad to see that you did (or are going to do?) the swap...In my opinion, the 3rd gen box swap is a great low buck upgrade to a first-gen. It has to be one of the top five "best bang-for-the-buck" mods for these cars.
The ratio is quicker, and the steering feel is much more "heavy" (ie like a modern car). ie no more feeling like you can steer the car with one pinky, like back in 69....
If you would like more info, Do a search on
www.pro-touring.com and/or
www.camaros.net and you will find a TON of information on this exact swap, part numbers, etc.
I would not hesitate to use the Lee adapter inserts, unless you really have your heart set on doing a power steering pump swap too...
Lee Manufacturing can set you up with the adapter inserts and coupler that you need with a quick phone call and about $60. (818) 768-0371.
Additionally, David Pozzi has a great page with tons of info on first gen steering upgrades here:
http://www.pozziracing.com/camaro_steering.htm
Good Luck!
-Rob