The old brush method will work a treat but only with the right prep and materials. 1970's brushing enamel is not the same as your B&Q front door gloss, chemically speaking. Good results were down to your estimate of humidity, air temperature, etc........and god help you if you added too much or not enough 'driers' to the mix........not much fun cleaning paint off a vehicle which 'bloomed' with moisture or just would not dry after 2 days. Brushing enamel is still available from specialist suppliers, if you want the look.