The VW camper van used in Serangoon Road has the registration plate SV1900. The movie was purportedly set in 1964, but this number was not issued until 1967.
Mandarin wasn't very commonly used for day to day conversation in Singapore during the 1960s. Regional dialects like Hokkien (Min Nan) were way more common, even amongst expatriates that spoke local languages.
Some of the telephone sets used are Singapore Telecoms standard telephone sets from the 1980's.
The character Amran is described as a police inspector, but his rank badges are the equivalent of a British General (4 star), and he wears them the wrong way round throughout; the crown is worn next to the collar.
Inspector Amran wears two bars of medal ribbons. There are duplicates of two ribbons - the ribbon with three white and two black bands and the one with three green and two black band. Each appears on both the upper and lower bars.