Good find! It does look like an F-1 Murray Eliminator. The F-1 is for the F Series frame, single speed. Murray frames have serial numbers that will tell you which model they are, so if you find the serial number on the non-drive side rear dropout and post it, I think I can decode it for you.
It has the Murray stripe decals on the downtube and seattube. Check out this one. I had the twin to this back in the day.,,,,,http://www.nostalgic.net/1968-murray-f1-eliminator