i have a gli 2012 as well,i wouldnt really recommend getting cng installed.that too for 85k.
the reason is that there is not much difference when it comes to cng vs petrol.you have to keep in mind that 3 days cng off bhi hey.so you will run on petrol as well which is going to reduce the savings at the same time.
then in near future,you cant really rely on OGRA for its plan of actions.so dont get CNG installed in a wow car like corolla.enjoy petrol and drive reasonably with planned trips.you will save well.
as for corolla ecotec,the head was modified for CNG usage.the petrol Gli has the old head which is still not very much compatible in the long run.(toyota walton guy told me).
if you save 3 Rs/km then you will have to drive 25000+ kms to just get over the cng kit price,then your actualy savings will start.
rest is upto you.all the best.