The amount of the unified pension payable to an employee, former employee or survivor shall be the sum of the following:
(1) The amount computed according to this chapter, exclusive of service credited under § 8801(6) of this title; plus
(2) The sum of the amounts computed, based on credited service as an employee, according to subchapter II of Chapter 55 of Title 29; subchapter II of Chapter 55A of Title 29; and subchapter III of Chapter 83 of this title.