435 horsepower in 1955.....

[Flathead]

Dynos can be a "little" off sometimes. However, with 17.5 lbs of boost on a 50% load of nitro, I'm sure there was some HP being made. I too would question the rods and the rest of the bottom end.

Didn't Barney himself run a similar motor at either the lakes or Bonneville? Small cid with a blower?

A good blower setup makes those old Flatheads forget their asthma problems.