GM / General Motors: '60 - '72 Chev 1/2 ton trailing arm geometry

Anybody happen to have dimensional data (or even better, engineering
data) for the trailing arm setup used
on these trucks? My Helm manuals list pretty good frame dimensions, but
I do not have data for this application. I have been seriously kicking
around the idea of building a 2x3 rectube frame using this setup for use
under a late 70s Chev passenger car.
This will be, of course, an extended project, but I'd
like to complete some decent CAD drawings prior to firing up the
Sawzall.

Thanks...
Mark