Ok, if I take your HTA as 74.75 considering the 0.25 degree frame tilt, your radius as 337 mm, then the trail is 52.0 degrees. Many commercial higher-end bikes today (most?) are pretty close to 60 mm. I think Nessism or Thylacine was suggesting a design target around that point as well?

I'd try measuring the fork rake with a different method, just to test. I'd say your number is plausible, but I'm not sure I understand your method. Did you get a string to be parallel to the steering axis? I'm not sure I see that you did, from your description. If you did, how did you sight it to know it's parallel?

This IS the hardest measurement.