I redesigned the trigger mechanism to accommodate an (I think) standard ballpoint pen spring. I didn't modify the trigger itself, just the housing. I also had trouble getting it to fit with the upper receiver, so I removed some material to have it sit slightly lower.
I corrected the pins to be better lengths and diameters.
I added a little flat cap to the crossbar pin, although it may break off when you remove it from the bed. I also left the pin deliberately long, it's so small I just clipped it to length.
All still prints as per the original instructions. Also, apologies on size+rotations. I redesigned the parts in Inventor and the export settings are always funky. In Cura I scaled 1000% and rotated appropriately