I am on a MTB too with stock tyres (one of which had a bad flat today, so I would be on patched tubes :) )
I have done the Krishnagiri stretch on the MTB - it was difficult - was my first 100+ attempt anyway, especially since it was raining hard that day - but I think in the cooler evening time and now with 3000 odd km on the legs, it should be easier (relatively).
I have no idea of most of the KGF stretch which from the recce reports so far and the altitude chart, looks on the comfortable side (relatively).
Considering the terrain is mostly friendly till Krishnagiri, you should be able to do 200 within 12 hours. Then you have 8 hours for around 100 km. Except for the climbs, which is probably 20% of the distance, the terrain is mostly gently rolling. Tired legs notwithstanding, you should be able to do an average of 13-15 on this stretch including your breaks - this is how I am convincing myself. See if it works for you :) Break it down into smaller rides and you should be ok - what worked for me in the last brevet is for every 20 km after the highway stretch, I gave myself 5 minutes idle time off the saddle. And with some fellow rides at the last stretch, motivation was ample.
In any case just go ahead and attempt it - lets see what happens, look at it as strength building. And my suggestion would be - from whatever little experience I have - do as much solo riding as you want in the initial stages. Look for company of strong riders, anyone riding better than you on MTB at that time, towards the last 100 km. A lone mind is very dangerous if you didn't know how to control it. It will give you a 1000 reasons to slow down, stop or quit. Dont let it be alone if you cant gather motivation from within.