Steve ,

The widebody mod. that I have required welding all the angled steel chromoly parts to the fuselage around the door openings. I think this would best be done before covering was on the fuselage. Also the door frames required a lot of tweaking to fit the new openings. I do love the extra shoulder room when flying with a passenger. Very much worth the extra effort. I have heard of a model 4 with an all carbon fiber widebody modification. They say it's really strong and of course would be much lighter in weight than my steel mod. but I haven't had the chance to see it up close yet.
The bump cowl may be slightly more drag but it really looks right on the tail draggers with the 912 engines. Your big tires may be a limiting factor but they are fun and that's what it's all about. Even with the tires you will see an increase in cruise and climb rates. The extra 20 hp. is nice to have without sacraficing much useful load. Hope the snow lets up. Sunny and 60's here now. 70's later in the week. Sorry , had to throw that in .