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.