To Swim or Not to Swim.....That is the Question!?!?!

It is certainly possible.  It really depends on how motivated you are and how quickly you adapt to the water.  However, it took me a lot more than a month get to the point I could swim 750 meters continuously.

You have 2 months if you start tomorrow.  Any chance you could get one or two days a week in the pool now?  I did some swimming as cross-training when I trained for my first marathon.

I don't know where you live, but there are likely a number of tris throughout the summer.  You could give swimming a try and see how you do.  If you are progressing slowly, you could look for a race later in the year.

I'm not sure why you wouldn't hit the pool now. I would guess if you are running a marathon you have the endurance, you just need to work on your technique. I would think several light workouts between now and the marathon would help you get your technique correct then after the marathon you can work on the swim endurance.

You might find the swimming to be a nice change of pace in your training routine.