Just do a search for pull/pull and there are a gang of threads on them. I'm sure Ken or Minn have done it with pictures. I make up my own pull/pull systems using different sizes of braided stainless fishing leaders and a Debro assembly I buy at my LHS. I think I have a couple planes with the system out in my shop and I can post photos for you with the parts. There are pull/pull systems you can buy too. It's not a must do thing though. With a good running well broken in .91 it will be a power house. That weight of plane will fly well with any good .60 to .91 engine. I haven't ever run the ST .91 myself so I can't really say anything about that engine. These days in the smaller glow engines I run the SK.91 for two strokes and OS, Saito or YS in that range for four strokes. I'm sure someone here or in the ARF forum has used the combo and would know more about it then me. I ran the SK .91 in a kit built Extra 260 about the same size only a bit more weight, about 8 pounds and it worked out perfect for me if that is any help. If you look up the Nitro PLanes 90 size Extra 300 and look at the specs I just assembled one of those with a Saito 100 in it, another good choice, as I recall it was about the same size and weight.