The stipulations shall be deemed applicable only to employees engaged in or connected with the manufacture, fabrication, assembling, handling, supervision, or shipment of materials, supplies, articles, or equipment required under the contract, and shall not be deemed applicable to employees performing only office or custodial work, nor to any employee employed in a bona fide executive, administrative, professional, or outside salesman capacity, as those terms are defined and delimited by the regulations (29 CFR part 541) applicable during the period of performance of the contract under section 13(a)(1) of the Fair Labor Standards Act of 1938, as amended.