I originally had the FE2 package on a 79 holiday coupe. I now have a 79 Holiday without the FE2 and I want to improve it. Should I look for original FE2 parts, aftermarket or ?

 

I would look for a '78 to '90 Caprice 9C1 for the front & rear sway bars. They're bigger than the Caprice/Impala F41 which IIRC is bigger than the FE2 bars on the Olds. Get the springs if you can, they are higher rate. The shocks I would do aftemarket.