You asked for an aerodynamic reason for the flap discrepancy and so here goes....
From long gone memory, is not the wing surface of the B55, from just aft of the leading edge until the flap itself rather high profile riveted and is not that of the B58 much smoother and more aerodynamic?
One regrets that the front garden provides access to neither machine to check this but it was a bit of a memory nuisance when transferring from one to the other in the good old days of barnstorming bush bashing.
