I went back to the owners manual - printed 9/72 for the 1973 model 164 - which shows a dashboard tach with a 6000 rpm warning zone---6500 rpm redline. Of course I realize that picture may not be the be all and end all answer. Further reading showed speed in gears 1-3 @ 1000rpm as 5.5, 9.3 and 14.6. Reading further still -- max speed recommended for gears 1-3 as 35mph, 55mph and 85mph. These figures work out to just under 6400rpm for 1st, 5900rpm for 2nd, and 5800rpm for 3rd.
BTW--the 6cyl. tach for a 260 shows a warning zone starting at 5500rpm--redline at 6,000.
I was incorrect stating the speedo in the manual as reading 200kph (must have been a 260 manual I also looked at) -- the 164 manual shows a 130mph speedo.
My wife, and then my son drove a '73 164 but I don't remember the redline on its tach--that was over 20 years ago. -- Dave