About 20 years ago I bought one from Golden State Pickup Parts. It was of excellent quality, looked perfect, and fit like a glove. Unfortunately they don’t list the item in their current catalog. Sometime around five years ago I pulled the automatic and installed a T10 4 speed requiring a new mat. I generally purchased my parts from Chevy Duty or American Classic Truck Parts, and for whatever reason I bought my current mat from American Classic Truck Parts.
http://www.americanclassic.com/asp/d...to&exyear=1966
It fits fine, but the quality is terrible. The surface is covered with cracks as if the mold was too cold, or the rubber compound was of poor quality. It looked the same the day it came out of the package, and should have been rejected and scrapped rather than sent to a customer. Unfortunately I lived 40 miles from town at the time and it was too inconvenient to send it back so it went in the truck. I wouldn't buy another one from them unless I could see it in person first. The defects can be seen pretty easily:
Depending on how important the original appearance is, here’s an older thread about the LMC floor mat that covers the entire floor of the truck:
http://www.chevytalk.org/fusionbb/sh...hp?tid/161727/