Roll...I just noticed you had pics in your photo album. Not too bad of looking '64. Are you planning on using the stock engine or replacing it? For '63 & '64 parts are numerous. As TM454 stated, check out www.chevytalk.com
and find the '61-'64 Fullsize forum. A wealth of knowledge on that year of ride. When I get a chance I'll post a few places where you can order parts new and used. Also just do a search for '64 Impala parts and you will come up with a ton of places. I like this search engine www.ixquick.com
as you can open multiple windows. One thing to remember is '62-'64 have quite a bit of parts that interchange. Your trunkpans, floorpans, etc, all interchange. One thing you will want to do is crawl underneath and in the area of the gas tank, look at the body mounts. These are commonly called box supports as they are boxed in. These quite commonly go bad and will need to be replace also if rusted out.