were can I access free printable or downloadable service manuals
I am assuming you are looking for service manual (not the owner's manual).
If that is the case I would be cautios download anything online as most sites offer pirated copies + viruses.
Your bet to get exactly what you want is to buy it from eBay. It is much safer than a random site. Here is a cheap service manual for your Impala listed on eBay.
Hope this helps.