RE: Two .46 engines... what size plane?
I think the LT-40 will be fine. I have a pair of OS .46LAs on a twin and they aren't going to pull the wings off unless you start doing crazy things which would probably kill the plane on a single engine. You are talking ball bearing .32 power here. I like a 10-7 or 11-5 prop.
I would strengthen the center wing and add some bracing wires on the tail. If you get the CG right, I'd use weed eater line. I use that a lot on planes. It weighs next to nothing and will keep your tail from breaking. If the plane is nose heavy, I'd use 2-56 rods just for the extra weight.
On the LT-40 with extra power, you'll need to shim up the trailing edge of the wing. I would jack it up 2 popsicle sticks or about 3/16". This should keep the plane from climbing at full power.