This is a good site for information on HK firearms but not a great site for information on how to build them.
For build information head over to Weaponsguild.com
Look in "The Builders Bench", and you will see a "CETME/HK" heading. Click on that and you will find a wealth of
information on HK builds of all types.
Once you complete your build please post a range report and some before, during and after pictures.
I'll wish you good skill on your build as luck has nothing to do with it.