Welcome...
That information is covered in in Paul's plans here.
www.seabreeze.com.au/forums/Land-Yacht-Sailing/Construction/Build-a-Landyacht-Lake-Lefroy-Mini-Yacht/ Check out the rake and trail setup halfway down the page. This will get it set up correctly.
The steering head rake angle isn't important as long as the trail is set up correctly. There is a bit of leeway and they will still work. Just it is best to get it as correct as you can manage.

The first one takes some time to get it all set up right.
Cheers