Sorry to hear about your problems. I bought a used MM exhaust like yours and had the same problem. I am quite handy with the spanners but I needed to fit it about three times to get it to clear the frame and even then ONLY JUST. The pipes also wanted to rest on the engine oil filter housing.

I got it to fit by pushing it away from the engine and frame and then tightening it all up and finally the silencer. Its not really how I think you should fit an exhaust as I have always been taught to work from the front back to make sure there is no tension in the system when it gets hot etc. As my system is used and NOT mint and is on my bike for off road so cosmetics dont worry me - I bashed a bit of a flat on the link pipe to clear the frame a bit more. You cannot see this at all when fitted.

I was also disappointed to learn from two other members of this forum that their cans had been bashed by their brake calipers when the suspension had bottomed out.

Lastly, the exhaust is meant to run without any fuelling mods. Mine pops and bangs badly on the over run when the throttle has been shut off abd the bike is still moving. I have fitted the Kev fuel mod which has slightly improved it but it is still annoyingly bad. All in all it is probably the worst quality and running exhaust I have ever used. Unfortunately as someone else has mentioned the only alternatives are more than double the price and there is no point me paying that to use it off road!!