Ummm. I had this same question not to long ago. I asked a buddy if it was a good idea for the longest swingarm possible. I was looking at a +16 for my 593cc Cheetah. This is what I came up with;
Although, it seems like a great idea to go with a longer arm, it will end up hurting you in the end. You DO NOT want to go over a +14 swinger. The reason being is, you have more chances for the long ass chain to jump. Even if you have a tensioner on there, you might as well forget it man. Plus, even though you have the power with that engine to drive that long of a swingarm, you are going to be robbing yourself of a lot of power! If you are hell bent on trying it, give it a whack and let us know how it goes. There is a reason that +16 arms are pretty cheap.
I strongly suggest that if you are looking for more length, you modify your chassis first, OR get a drag chassis. For that motor, I think it would look great in an extended chassis anyway.