(a) Arrangements for wage continuance during disability, in effect on April 13, 1949, may be accepted as an existing plan, provided such plan formed part of the employer's regular contract of hiring, either under written agreement or by established custom and practice.

(b) A wage continuance plan in effect on April 13, 1949, but not then under written agreement, may be accepted as a plan if it is reduced to a written agreement and proof satisfactory to the chairman is submitted that the plan was actually in existence on April 13, 1949, as the employer's established custom and practice.