I am very interested in your project, as I have been thinking about doing something very similar.
Trough reflector to heat gas or liquids to supply heat for a multi-cylinder stirling engine electrical generator.
Is your reflector stainless steel?
I purchased about eight hundred square feet of reflective mylar a couple of years ago to use as a reflector, but got sidetracked after some surgery.
There are several people on this site who are interested in this type of project. Maybe you should start a thread on your build. I know of one person (Greybeard) who is also working on a solar dish.