Traning for 2x250km in 4,5 months
You don't say how young and foolish you are.  Many years ago, at age 17, I rode a double century (a little over 300 km) with about that much climbing with no training at all.  I had never ridden more than 50 km in a day.  The weather was much cooler than 30C.  The hard part about the second trip would have been psychological-I found the double to be much more than was fun.  I rode a number of centuries, 160 km, afterward and found them fun, but the double took 16 hours.  I was on a decent 1960's road bike. If you have done 200 km already, you have a good idea what it takes.  You can get a lot stronger in 2-3 months of training.  Go for it.