Need help with demensions for a glasspack
 

I want to buy a glass pack for my 2002 Blazer. I'm only 16 and have put dual exhaust on a 74 Amx before. So im a little familiar on this, however not the dementions on what I should get. I cant take the muffler off the car and see because I have to drive it daily. I see that on mine, the tailpipe is welded directly to the muffler and is ran over the axle and out the back. However on the front end of the muffler there seems to be a gasket or something, not completely sure. I was looking at putting some thrush glasspacks on, trying to keep it under 25 dollars. If anyone could give me the dementions of the muffler I will need that would be great and if I will need an extention to bolt to that gasket or whatever. Im not worried about the tailpipe. I was just going to dump it. Anyway thanks in advance. All help is appreciated.