I had a MAC 4-1 for a very short time and just didn't care for it....made the bike sound like crap IMO....so you're not missing much.
This exhaust you bought looks alot like my Jardine exhaust, although mine is a 4-2, not a 4-1....the muffler certainly looks like mine, though.
Is there any particular part that isn't lining up? With the head pipes loosely attached to the engine, can you get them to meet up with the collector on the muffler?