The distance from the center of the cowl opening to the side of the cowl is a tad over 4 1/2" not much over though. The dimensions from the approx. location of the center of the cylinder of an RCS140 and the dim. from the beam mount to the top of the ignition cap when mounted (from the engine dimensions shown on the RCS web site) is 4 1/2" to the side of the cowl on the inside. The distance from the center of the shaft on the G26 is approx. 5" I checked it again last night. I don't remember the exact dim. just laid my tape on it and knew it was too big without cutting the cowl. It's obvious the inverted mount will not work either without cutting the bottom out of the cowl. There may be some out there who don't mind cutting but i'm too scale oriented. The RCS140 will just fit with a side mounted engine but if you want to stay with gas and consider the 140 I suggest you do your own math and not take my word for it. I'm still considering that engine if I stay with gas unless I get an awful good deal on a nice O.S. or Saito twin in the 1.20 to 1.50 range. Hope this makes sense.