Thanks for your input guys, The OS .46 is going in. Guess I will just cut out a hole for the stock muffler and hang it out 1 side like the plans show. I'll just be sure to take pictures of it from the left side I have had very little time to work on it but I have re-shrinked the covering and fitted the wing up to the fuselage. Although the quality of the construction so far could not be better the covering is a little rough. I would not be proud of the covering job if I had done it. The main reason for this problem is the holes for the aileron servos and where the the tail feathers are mounted have already had the covering removed and the edges were not rolled over in the aileron bays. This makes it impossible to shrink the covering wrinkle free on the elevator and the bottom of the wings as the covering will just pull away leaving bare wood around the open bays. I wound up having to cover over the bays with some ultra-cote and then re-shrink it to get the covering a little tighter.
This is approximately eighth R/C airplane and my first ever ARF and I must admitted its kinda of fun opening a box and seeing most of the work already done for you. However, I really enjoy gluing, sanding and covering so the work that is left installing the engine, servos and running the control rods is actually the least enjoyable part of the hobby for me. Assembling this ARF will be a nice break (even if its only for a week or so) from building my current project which is a Sig King Kobra.