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I made these years ago.  Closed-cell foam - one on each down-pipe and held in place by a small rubber-band.  They hold the "exhaust pipe holders" in place for assembly.  When done - cut the rubber-band and removed easily. 

 

The "split-keepers " ?   A thin strip of electrical tape, stretched modestly and wrapped around them holds them in place. The tape can be left on. 

Exhaust gaskets?   A bit of Silicone grease holds them in the (clean) cyl-head port.