personally what i would do is find some place that is able to fab up your exhaust with stainless steel pipe as being up in main you must have some good rust up there. for the muffler i wouldnt touch eather one as glasspacks are not my thing and they burn out. as for the flowmaster they may sound nice but are restrictive and if you dont get the stainless steal version will only last 2 years. a magnaflow would be the best as they are full stainless steel and reversible.
Dynomax Performance 54020
custom tail pipe
you may be able to run that tailpipe you listed if you use a reducer like this but you may need a section of 3" pipe to connect it to the muffler.