I know running in 40+ temperature sounds like a super endurance effort (thought the temperature usually is in late 30's these days, during the day). Its not really so difficult. Its just a question of getting used to it (human body can get used to almost anything!!), getting mentally tougher & some extra hydration. In this sort of heat, with 60+% humidity, I would recommend about 500ml of Gatorade or similar drink for every 1hr 15mins, and if you are doing something more than that, then some high carb bar would be required in addition to the hydration. In this weather, water is not just good enough for any distance beyond 40mins and if you do try to attempt it, ensure that there is someone to take care of you, should you suffer a heat/sun stroke (yes that sounds quite alarming, but what I am trying to say highlight is the fact that at the first signs of exhaustion appearing, without any legs muscles getting strained, is a sure sign of exhaustion). And yes, another must is a good pair of sun glasses in this sort of heat, as a sun stroke is very possible without it (esp. with improper hydration).
I did a good 6km run in 33minutes on Wednesday and then took the rest of the week off, as I had a holiday on Friday (surprisingly good Friday seems to be big these days in Bombay). I managed my 11km run today in a little over 1hour, quite well, given the conditions (heat, heat and more heat), plus the late start - 8.30 in the morning (wanted to catchup on sleep after a late night out with friends). I am now quite confident that I will be able to do lot better on the Sunday long run, hope to do atleast 15km with an early morning start.