Investments may also be made in first mortgages on improved real property which are insured by the Federal Housing Administration under the National Housing Act, are guaranteed by the United States Department of Veterans Affairs under the federal Veterans’ Benefits Act of 1958 and any amendments thereto, or are otherwise insured or guaranteed by the United States of America or any agency or instrumentality thereof so as to give the investor protection essentially the same as that provided by such National Housing Act or federal Veterans’ Benefits Act of 1958 and any amendments thereto or in notes, bonds, or debentures fully collateralized by such protected mortgages.