you should keep an eye on www.hemmings.com type this in your web search box, there were 18 mostly 2 doors from last months online magazine, hemmings motor news has deep world wide roots in the car world, and is the first place I would go, bring your check book, you want a nice clean 4 door, figure 10 to 20 grand should get one sweet ride.I looked on classic car trader www.autotraderclassics.com and found several more, mostly two doors, again prices are from 10 grand and up the 67 and the 68 had similar body styles, off hand, if you are looking for something as a daily driver, the 327, the 350, and any of the big blocks are best, chevy had a 305 and a 307 neither one of these engines, is worth much. and not very good. (it drops the price a lot too) the best small block would be the 327 my favorite chevy motor chevy motor for the big block is hands down a 427 I did not see a lot of four doors but that's ok cars come and go everyday, If your patient and sign up with the hemmings online magazine to get the current ads, you may find one nice four door from 6 to 10 grand, depending on just how nice a impala you want. best of luck hope this helps