I am building my own semi triggers and sears as I really want to get my last two kits together. I am going to use Hedgehogs design as it has proven very reliable (6,000 rounds through my FN32 and 3,000 rounds through my FN30).
The Hedgehog design uses a paddle style toggle in the trigger bar arm and the original sear modified with a vertical post for actuation and a plate riveted on to attach the sear into the widened bolt slot. I will post some pictures as it progresses. His design overcomes the extra vertical thickness of the trigger bar arm by removing a slot out of the top plate and making a small corresponding notch on the rear site base.
The only thing I am going to do differently will be to insert a block into the top plate to prevent the full auto trigger from being introduced into the gun. Kris did not do this and instead blind pinned the semi trigger into the gun permanently which to me is undesirable from a maintenance/repair stand point.
Here are some pictures so far,
Cut front off full auto trigger bar-
Weld on some 3/8" bar stock for the front-
Cut out top plate for both full auto trigger blocking piece and semi trigger bar clearance (left modified, right original) -
Cut step on side of trigger bar to prevent over travel (Kris had this step on the cocking lever side I am putting it on the outside of the gun).
I will post more pictures as it progresses.