Keith, the KS pipes are very good and I have owned and used the larger one. This one might go well on the 90,
http://www.krumscheid-metallwaren.de...EN&anr=1015-4#

Macs pipes are pretty standard as well. http://macspro.com/tunedpipes.asp They are much more common on glow engines.

I believe Dick Hanson works for Ed Skorpa and he makes carbon pipes for small pattern engines.

The question of piping this engine might be better asked to an active pattern flyer like Todd Blose or his Dad.

Joe