Daniel, I would go for the LA.40 in the arf. As for the triangle stock, you can access this through the tank compartment prior to installing the tank. There is no need to rip anything open. I suggest using bolts rather than screws to hold the gear on. As John states the covering is an issue on these and will come loose and eventually blow off. I addressed this early on by applying small strips of clear over the leading edge for example. I used a 1 " piece of covering the whole way. I had to do this around flap areas as well. I used all pin hinges on mine. You will find what appears to be a slit the whole way down the flaps as well for easy installation of the ca hinges they provided. I wouldn't use those and I would seal that covering real well prior to gluing on the flap horn. It's a heck of a lot easier to iron on strips around the flap now rather than on the model. I see some of us don't prefer the Fox.35 as some claim it's not powerful enough. I was just stating that's how Dee Rice designed the plane to be powered with which is why I did the same. I don't regret it as my plane has brought me 3 first places in Intermediate last year using the Fox.35. The Brodak .40 is an excellent choice for its weight , power. Bill though has stated above that he used the OS35S. A fellow club member uses the OS 35S in his and it flies tremendously. I wish I had that engine in mine. My point of using the Fox was merely based on the cg as well. The plane was designed for an engine weighing in the 7.5 oz. category. If you decide to use others your going to have to balance it accordingly. The arf uses a 4" bellcrank. THIS MAKES FOR SLOW CONTROLS. I've seen even experienced flyers take this arf out and almost plant it on the first flight. To compensate for this they were using the wide spaced Hot Rock handle. I dug back into the plane and moved the pushrods closer to the center of pivot and higher on the control horn. I personally didn't care for the slowness. Others love it, but not me. I just wouldn't suggest using an engine that puts out a lot of castor oil residue such as the Fox or OS 35S due to the covering on these models. I've had the entire wing panel of coat come off on the Oriental due to the covering getting oil soaked and releasing. I truly feel out of all the arf's I've built the Oriental gets the biggest thumbs up in my book. I have about 150 flights on mine with the LA.40 in it. My son used the plane for several years and now I have it. In addition to the tank you purchased. I had trouble making the pattern with 4 oz.s of fuel in mine. I had to lean the engine more than I liked and this makes for fast flying which makes the maneuvers hard to do. In order to slow the plane I had to now go to longer lines to slow the plane with the leaned out needle setting. I should've just changed the tank which was eventually what I did. The good thing is, changing the tank out is very easily done in this plane. My La.40's, and I own three all use more fuel than any other LA.46 in our club. This may very well be a venturi size issue. The fellows in New York use Bru Line air filters which restrict the venturi which in turn makes you have to lean the engine for more power. This gives them not only the power they needed, but the economy as well. I never tried their method. I went to a larger tank. I now use a 4.5 uniflow. I think were all aware of the fact that there's been all kind of different size venturi's made available from OS. It may very well be possible mine is too large. I haven't measured it so I can't comment on what is in the engine. You may also be at a different altitude as myself.