Flange's do fail. I will measure tonight against an A, will post the difference. I modify for better performance but don't race. In fact I'm quite happy with the power my modified flathead A puts out ( basically double of stock using my seat of the pants dyno), just want the long distance touring capability the B offers, I don't chase the dragon...yet
.Plan on using a stock B flywheel behind the C crank and use modern fasteners with loctite to retain the flywheel. No lightened flywheel for this engine, want the mass for smooth drivability.
For racing(someday I might bump my head) I do have a late B that was bored to 4.060 and has balanced rods. I also have a 31 A block bored to .125 fitted with a beavertail A crank. The A block would get the lightest flywheel I could find, make a hillclimber..using the lightest rotating group I can muster insures fast application of torque, It might not last but will be fun while it does.