Hi Michael, You will want to check with Eric Schade but I'm balking at the idea that Western Red Cedar would not make a suitable shear clamp. I built a 17' S&G boat. The shear clamp (in this context) is mostly a gluing surface and really doesn't have to be that stout; the adjoining planes will act to reinforce each other.

I'm reading the Adirondak Guideboat book now. Builders have been using softwoods this way for generations. There are stronger softwoods out there but WRC is very strong and, for this application, it's splitting hairs.