All boards, commissions and heads of departments of the State Government may invest moneys or funds in their possession in the following securities:
a. Bonds of the United States of America.
b. Bonds of the State of New Jersey, or of any municipality thereof, including school districts.
c. Mortgage bonds or notes secured by property within the State of New Jersey and insured by the Federal housing administrator.
No investment of such funds shall be made where the total debt of any such municipality, including the school debt, shall exceed thirty per centum (30%) of the assessed valuation of all the real and personal property therein; but in ascertaining the total indebtedness, credit shall be allowed only for such moneys or property as shall be in the sinking fund.