I have seen the stock tensioner mounted upside down (pushing chain down under the brake arm)
I have also seen them mounted on the top chainstay pulling chain up n over the brake
you should search occ's here and see what others have done (some really good ideas to be had )
hope that helps
Take the tensioner and a hammer and beat it flat. Use longer bolts, Good ones. Mount under the frame. It's hard to get right but worth the effort. I make tensioners for most bikes. If you need one let me know. Check out 2 stroke kits thread under Wimpy parts, I sent pics.