If this is the kit you are looking at you'll still need to source some lower a-arms and tie rods:
http://www.bd-xtreme.com/index.php?id_product=26&controller=product&search_query=a-arm&results=93
FYI the spindles they use with that kit are considered by some to be a little on the weak side. I had that setup on my sled for a couple years and bent one and broke another. I've got it on the shelf with good spindles I would sell you cheap. Generally with the Cats you can narrow the stance by 2", have the spacers installed in the shocks, and everything will be correct geometry wise. Some like Suzzy-Q narrow the stance by 2", leave the shocks alone, and it works good for them. Sometimes this requires washers under the tie rod end to keep the rod from hitting the lower a-arm on full shock extension. So narrowing your stance 4" from 42 to 38 will require spacers to be installed at a minimum, and your shocks will be a little long still, but probably still work. Get ahold of a shop like Gas Shock Repair, The Racin Station, or Carver Performance that is familiar with the mods needed to confirm. My original comment I was thinking your year HCR had a 40" front end so a simple spacer would work to run the 38", but after I looked it up the spec sheets say they are 42" stance.