You can also get them through Jegs or Summit.
I installed a poly set on my 73' Coronet about month ago when I did the entire front end and the car stiffened up and handles much better. Shocks are important with these poly units. I went with KYB muscle car shock for a sturdier ride.
Important: After a little break in period, you'll get past the jittery stiff ride and then it will settle in.