the round "sanden" type compressor is easier to package than the old v type pump, plus it is almost half as heavy. all the heat/ac kits offered for retrofit are packaged with the sanden pump for those reasons. unless you are restoring something, the new pump is the way to go. also, unless you are real handy at fabbing stuff, the kits are the only way to go. you will be time and money ahead. there are tons of little things needed to make a "mix-n-match" system work. just my opinion.