Mini Bulkhead Clearance.

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FWIW, I managed to get a Minispares LCB exhaust system, slightly modified, into my Mk1 Scamp.  Removing or refitting the manifold was the sort of job where you run out of swear words and have to make up some more, but just possible without actually taking the engine off its mountings.

My Mk2 has an MG Metro exhaust, which just clears a solid bar which connects the otherwise unbraced members - inriggers, I suppose you'd call them - that rest on the FSF towers.