[35topdown]

The clutch disk could also be bent. Easily done durning installation or shipping. The excessive runout will cause this problem . The pressure plate only lifts the plate about .040" off the clutch disk when released. So any runout over .040" will cause it to drag. An incorrect adapter plate thickness could cause the input shaft to drag on the crank, as already suggested. I owned a clutch shop for 30 years and saw this many times. Whenever we built a clutch, it would get spun on an arbor shaft to check for runout. They can be easily straightned by hand. Just use some chalk while spinning it to find the high spots. Another thing to check is the release bearing travel. Once the bearing touches the fingers on the pressure plate, it requires about 3/8"-1/2" travel to release the clutch. Some brands of disks also have the retainer rivets that rub on the flywheel. I don't think the flathead flywheel has this problem, but it it something to check. I assume you did not put the disk in backwards. The spring retainer should go to the rear, towards the pressure plate. Your getting lots of good advice from the forum, so you will eventually get it figured out.
Richard