The hardware arrived so I could finish the improved seat mechanism.
The final solution was a combination of 1 blind rived, 2 AN3 bolts with nylon washers and castle nuts with cotter pins:
The bolts were a bit too long, I removed the extra length with a grinder and added some AV30 for corrosion protection:
I followed the advice from Sling builder Alois and added an additional bracket so the mechanism could be used with 2 fingers:
Perfect now:
With some LPS2 I greased the moving parts.