This is probably the last instalment of MG routes from Delhi to the major cities in South India. Trivandrum came on BG in late 1975, so this time we imagine a journey in 1970. One could also imagine a link express from Quilon to Ernakulam.
This comes to 3249 km, which is just over 2000 miles. Probably it would take a week.
In 1970, TVC was indeed the southern-most station in India as its latitude was less than that of Tiruchendur, which remained on MG until 2000 or later.