With the near-complete removal of metre gauge from all important routes starting from the late 1970s, it would be a surprise to younger railfans that as late as 1976 it was possible to travel from Delhi Jn to Bangalore City wholly by metre gauge. (At that time there was no train from Delhi to Bangalore, though there were through coaches on the GT Express and Madras/Bangalore Express. The Kerala-Karnataka Express was yet to appear.)
There was, of course, no such MG train but by a series of reasonably good MG expresses it was possible to make this journey of 2389 km. The BG route via Madras would be a little longer at 2536 km.
Let us begin our journey from Delhi Jn. I have taken the distances from the 1976 All India Time Table. Spelling of names are from that period. Inflated distances were being charged between Khandwa and Hingoli, so I have taken actual distances.
Between Rewari and Phulera I have taken the route via Ringas rather than the better-known route via Jaipur, as the former is shorter.
This route passes through DL, HR, RJ, MP, MH, AP and KA. (Also TG which did not exist then).
Delhi-Madras has been covered here: https://abn397.wordpress.com/2021/09/18/delhi-to-madras-by-metre-gauge-in-1976/
Madras-Bangalore has been covered here: https://abn397.wordpress.com/2022/01/02/madras-to-bangalore-by-metre-gauge-in-1976/
Those who have timetables of 1976 or thereabout can work out suitable combinations of trains to cover this route. Examples could be Delhi-Ajmer, Ajmer-Secunderabad, Secunderabad-Bangalore.
Compare this with the BG route via Madras.