The legislative body of any county, city, village, township, or other local unit of government may purchase on executory title retaining contracts, or finance purchases by chattel mortgages as security for the purchase price, any fire trucks and fire fighting apparatus and equipment and pay for it out of the general fund of the municipality. However, contracts or chattel mortgages shall not provide for payments for longer than the estimated period of usefulness of the property being purchased and in no event for longer than 6 years. Contracts and chattel mortgages, and the purchase of property under this section, are not subject to the revised municipal finance act, 2001 PA 34, MCL 141.2101 to 141.2821, but are subject to 1933 PA 99, MCL 123.721 to 123.723.