I made a trigger Dyno almot 5 years a go I just cut up a tapco bent blank that was exactly the same as what I was using and cut away any thing that wasent nedded so i coluld gring ,flile poilsh and test with out dissasmbly It cut the time to work a trigger by over 75 percent. some were i posted on it a few times. I did see were a guy had a plate that held the componets but it really didnt do much that my $9 set up did and I know it was the same as what I was building.
Somewhere I saw a picture where someone had bent and drilled some sheet metal to make a working model of an AK trigger group that could be examined from all sides. Something like that would help you verify the angles on the hammer wings and trigger hook.