If I remember correctly from installing mine, the spring goes in the hole in the detent. Then insert the spring-end of the assembly into the sear block with the spring pointing forward (towards the barrel). The notches on the safety lever will mate with the V-shaped part of the detent. I may seem strange, but at this point there is nothing holding the detent in place in the left/right direction - the safety lever will do this once it's all put back together. Make sure the detent can freely move front to back - my MP40c had a small burr in the sear block that prevented free movement, but a small file took care of that and now the safety has a nice positive click when engaging or disengaging.
If you still have trouble, I can pull mine apart and take pictures.
