Mike, You are probably going to get as many different opinions as there are responses to your post. I have bashed three sport/pattern planes to twins: Midwest Strikemaster, Kaos, and Direct Connection Sea Fury. All but the Strikemaster were tail draggers. Only aerodynamic change I made was to add about 20% of wing area to the middle of the wing to deal with the extra weight. I have never done out thrust on the engines. I did not increase the area of the tail group on the SM or Kaos. I went to a twin tail on the Sea Fury bash. (photos may still be here in a thread called obscure Russian bomber) Area probably increased.
I have a Handley Page O-400 twin WWI bomber that is a big, slow model somewhat akin to your Telemaster. 120" span, two ST 90's, Clark Y airfoil. Flat bottom of airfoil, stab, and engines all at zero degrees. It flies like a big trainer.
Based on what I have done I would suggest you place your engine nacelles under the wing to get the thrust line closer to the original design. That should maintain the original flight characteristics. I have found that a twin tail, like the Sea Fury bash, O-400, and an Me-110 I had helps with rudder control by having the rudders in the prop wash. Only other "words of wisdom" I have are to make sure you do not compromise the wing spars.
Chuck
