I asked my friend who know about this, I can conclude that tuk-tuks that we are commonly seen in Thailand are Daihatsu Midget DKA, produced between 1959 and 1960.
The tuk-tuks we see in Ayutthaya and Phitsanulok are 2nd gen, produced between 1959 and 1972. Thai people often jokingly called the frog-faced tuk-tuks.