New best so close.....

Try going up a 1/2 round on each of the 6 adjusters( add static pressure) and see if the 60' get better( if they do ) go up another 1/2 round till the 60' start falling off from wheel spin. Then go back a 1/4 round. Spinning 20' out is probably the suspension and chassis and shock set up more than the clutch( unless you are to light on the static pressure and real heavy on the centrifugal weight on the 3 levers and driving into the centrifugal weight to soon)
My 66 Dart weighs the same as your 66 ( I took a little over 90 pounds out over the winter to get it down to 3415) I am running a small block with 4 1/2 turns on the adjusters which is 675 pounds of static base pressure(150# per turn) and 13 grams of centrifugal weight per lever(39 grams total) which adds 1160# at 6500 rpms plus 675# base for 1835# at shift point. I dropped my launch rpm from 5000 to 4500 my last time out and went two 1.48 60' ( usually in the 1.5x 60') shifting 2nd gear before the 60' clock. That dropped my starting line pressure from 1186# to 1066#( that is base and centrifugal add together) That's with a 9x28 slicks, 4.30 rear gear, and 3.04 first gear in a DR-4 Jerico Cal-Trac's in top hole and shocks set at 9 clicks rebound 5 clicks compression, 14# air in slicks at Lebanon Valley.
Your car makes a lot more power than mine does so it's going to need more clutch pressure. I have talk to you before about these clutch set ups, but I don't think I explained it right so you could understand the set up. If you go to BlackMagicClutches on the internet he has two videos on his web site that explain how to set these clutches up better than I can. Good Luck to you and with a little more clutch and chassis tuning I am thinking deep into the 9's
P.S. When running the car if you see the 60' starting to get slower once you have the clutch set for best 60' add an 1/8 to a 1/4 turn to the base for disk ware to keep the clutch pressure the same for consistency.