Until perhaps the 1970s-1980s, the east end of US 266 was in a different location than its current terminus. Originally US 266 came from the south on 3rd Avenue. Instead of the current diagonal through town, it's likely that US 64 used 8th Street and Culwell. If so, then US 266 would've ended on 3rd Av at 8th St:
http://tinyurl.com/o9da7bz
By 1936 US 64 had been changed to follow the diagonal alignment, so US 266 was extended slightly north. Traffic split at a wye-junction, so there were actually two endpoints, depending which way you wanted to go on US 64:
West wye junction: http://tinyurl.com/pfay9am
East wye junction: http://tinyurl.com/nrc5kfm
Google Street View coverage of this area is lousy, so it would be great if anyone is willing and able to shoot some photos of these junctions. The photos would be used on this page...
http://usends.com/60-69/266/266.html
...and you would be credited for your efforts. Thanks!
I'll try to head down that way next time I go to Arkansas. It's barely out of the way at all.
Ironically, at approx. the same time I was writing the original post, a Google car was making its way through the streets of Warner. Its photos are now online, and they are of decent enough quality that I have used them to update my page with the historic endpoints: http://usends.com/60-69/266/266.html