If you want more low end torque then go up teeth in the rear. And going up in teeth in the back or dropping teeth in the front is going to put more stress on the chain.

Go on ebay and buy a 520 conversion kit. Its usually 150 bucks for a 520 chain and a front and rear sprocket of your choice (in # of teeth that is).

Buy me on ebay...............weeeeeeeeeeeee