I appreciate the pics,... but, I'm not familiar with the Jardine... so, I'm nor gettin' much... (yer' clamp looks beefy enough)...
... but,.. here's what I do with other muffs...
Loosen, everything... keep the bolts in place, but loose...
Then, tighten at the head first,... then, the muff clamp,.. then at the end... (there is a bit of flex available)...
If that don't work... buy an extra exhaust gasket,... and double it up... I have two on mine...(they are crush gaskets, and if the first one is too crushed, it can't seal)...(a new one might work alone,.. but, I use two,.. to make sure I'm out far enough for the bolts to pull tight)...
DON'T overtighten!... and use a bit of anti-seize on all exhaust bolts...
From there,.. if the muffler bolts just won't line up,... drill new holes... or send it back... your choice...
JMHO...
...